The list of steps i performed was missing the "add"-command.

The original error occurs when I type:
cd \Users\myuser\Videos
bzr init
bzr ignore desktop.ini // after the first try I just left the existing .bzrignore in place
bzr add .
bzr commit

The "add"-command adds the large files and probably causes the crash.

To answer your question, I just deleted the ".bzr"-directory and started all over again, this time adding only a small file (.bzrignore) but leaving the large files in the directory. this works:

"scenario 2":
C:\Users\carsten\Videos>dir
 Volume in Laufwerk C: hat keine Bezeichnung.
 Volumeseriennummer: AED8-C42B

 Verzeichnis von C:\Users\carsten\Videos

06.01.2011  18:28    <DIR>          .
06.01.2011  18:28    <DIR>          ..
05.01.2011  18:34                13 .bzrignore
05.01.2011  18:26    <DIR>          1987-04-26 - Kinderkommunion Carsten
05.01.2011  18:25    <DIR>          1991-09-25 - Kim
05.01.2011  18:27    <DIR>          1998-11-13 - Goldene Hochzeit
05.01.2011  18:26    <DIR>          19xy - Meran RTL und ARD
05.01.2011  18:25    <DIR>          2001-09 - Cala Ratjada
               1 Datei(en),             13 Bytes
               7 Verzeichnis(se), 208.388.423.680 Bytes frei

C:\Users\carsten\Videos>bzr init
Created a standalone tree (format: 2a)

C:\Users\carsten\Videos>bzr status
unknown:
  .bzrignore
  1987-04-26 - Kinderkommunion Carsten/
  1991-09-25 - Kim/
  1998-11-13 - Goldene Hochzeit/
  19xy - Meran RTL und ARD/
  2001-09 - Cala Ratjada/

C:\Users\carsten\Videos>bzr add .bzrignore
adding .bzrignore

C:\Users\carsten\Videos>bzr commit -m "..."
bzr: warning: The commit message is a file name: "...".
(use --file "..." to take commit message from that file)
Committing to: C:/Users/carsten/Videos/
added .bzrignore
Committed revision 1.

So, nothing bad happens when I leave the large files unadded.

"scenario 2":
To discover what happens with other operations with the large files added, I did this (after first deleting the ".bzr"-directory):

C:\Users\carsten\Videos>bzr init
Created a standalone tree (format: 2a)

C:\Users\carsten\Videos>bzr add "19xy - Meran RTL und ARD"
adding "19xy - Meran RTL und ARD"
adding "19xy - Meran RTL und ARD/Meran.MPG"
adding "19xy - Meran RTL und ARD/Meran.divx"

C:\Users\carsten\Videos>bzr status
bzr: ERROR: exceptions.OverflowError: long int too large to convert

Traceback (most recent call last):
  File "bzrlib\commands.pyo", line 917, in exception_to_return_code
  File "bzrlib\commands.pyo", line 1117, in run_bzr
  File "C:/Program Files (x86)/Bazaar/plugins\loom\commands.py", line 203, in ru
n_argv_aliases
  File "bzrlib\commands.pyo", line 691, in run_argv_aliases
  File "bzrlib\commands.pyo", line 710, in run
  File "bzrlib\cleanup.pyo", line 135, in run_simple
  File "bzrlib\cleanup.pyo", line 165, in _do_with_cleanups
  File "bzrlib\commands.pyo", line 1132, in ignore_pipe
  File "bzrlib\builtins.pyo", line 301, in run
  File "bzrlib\status.pyo", line 168, in show_tree_status
  File "bzrlib\status.pyo", line 72, in report_changes
  File "bzrlib\tree.pyo", line 94, in changes_from
  File "bzrlib\decorators.pyo", line 140, in read_locked
  File "bzrlib\tree.pyo", line 1002, in compare
  File "bzrlib\delta.pyo", line 127, in _compare_trees
  File "_dirstate_helpers_pyx.pyx", line 1439, in bzrlib._dirstate_helpers_pyx.P
rocessEntryC.__next__ (bzrlib\_dirstate_helpers_pyx.c:12084)
  File "_dirstate_helpers_pyx.pyx", line 1712, in bzrlib._dirstate_helpers_pyx.P
rocessEntryC._iter_next (bzrlib\_dirstate_helpers_pyx.c:14846)
  File "_dirstate_helpers_pyx.pyx", line 1811, in bzrlib._dirstate_helpers_pyx.P
rocessEntryC._loop_one_block (bzrlib\_dirstate_helpers_pyx.c:15715)
  File "_dirstate_helpers_pyx.pyx", line 1136, in bzrlib._dirstate_helpers_pyx.P
rocessEntryC._process_entry (bzrlib\_dirstate_helpers_pyx.c:8198)
  File "_dirstate_helpers_pyx.pyx", line 872, in bzrlib._dirstate_helpers_pyx._u
pdate_entry (bzrlib\_dirstate_helpers_pyx.c:5834)
  File "_dirstate_helpers_pyx.pyx", line 824, in bzrlib._dirstate_helpers_pyx._p
ack_stat (bzrlib\_dirstate_helpers_pyx.c:5492)
OverflowError: long int too large to convert

bzr 2.3b3 on python 2.6.6 (Windows-7-6.1.7600)
arguments: ['bzr', 'status']
encoding: 'cp1252', fsenc: 'mbcs', lang: None
plugins:
  bzrtools             C:\Program Files (x86)\Bazaar\plugins\bzrtools [2.3.0]
  colo                 C:\Program Files (x86)\Bazaar\plugins\colo [0.2.1dev]
  explorer             C:\Program Files (x86)\Bazaar\plugins\explorer [1.1.2dev]

  fastimport           C:\Program Files (x86)\Bazaar\plugins\fastimport [0.10.0d
ev]
  launchpad            C:\Program Files (x86)\Bazaar\plugins\launchpad [2.3b3]
  loom                 C:\Program Files (x86)\Bazaar\plugins\loom [2.2.1dev]
  netrc_credential_store C:\Program Files (x86)\Bazaar\plugins\netrc_credential_
store [2.3b3]
  news_merge           C:\Program Files (x86)\Bazaar\plugins\news_merge [2.3b3]
  pipeline             C:\Program Files (x86)\Bazaar\plugins\pipeline [unknown]
  qbzr                 C:\Program Files (x86)\Bazaar\plugins\qbzr [0.20.0dev1]
  rewrite              C:\Program Files (x86)\Bazaar\plugins\rewrite [0.6.2dev]
  svn                  C:\Program Files (x86)\Bazaar\plugins\svn [1.0.5dev]
  upload               C:\Program Files (x86)\Bazaar\plugins\upload [1.0.0dev]
  xmloutput            C:\Program Files (x86)\Bazaar\plugins\xmloutput [0.8.7.de
v]

As you can see, it does not need a commit to break things, the "add"-operation was sufficient.

I hope this helps.