I'm experiencing the very same problem.

OpenOffice.org: 2.4.1 (same version as mentioned above)
Kernel: 2.6.24-19-generic #1 SMP Fri Jul 11 23:41:49 UTC 2008 i686 GNU/Linux
Distribution: xubuntu 8.0.4
CPU:    AMD Athlon(tm) 64 X2 Dual Core Processor 6000+

I had that problem on a Debian Etch amd64, too.

For me it's file-independant. It occurs with long-used Spreadsheet files as well as with blank spreadsheets, even with no document opened at all.

The frequency is somewhat irregular between 1-2 minutes.

This is what strace for the process is outputting at the moment the menu bar (file) is focused:

###### snip ######

gettimeofday({1219097455, 105051}, NULL) = 0
select(8, [7], NULL, [], {0, 0})        = 1 (in [7], left {0, 0})
read(7, "\2@\306\203\360\f\236$;\1\0\0\37\0@\4\0\0\0\0N\5\212\2"..., 4096) = 64
read(7, 0x80db96c, 4096)                = -1 EAGAIN (Resource temporarily unavailable)
gettimeofday({1219097455, 105343}, NULL) = 0
read(7, 0x80db96c, 4096)                = -1 EAGAIN (Resource temporarily unavailable)
read(7, 0x80db96c, 4096)                = -1 EAGAIN (Resource temporarily unavailable)
gettimeofday({1219097455, 105473}, NULL) = 0
gettimeofday({1219097455, 105529}, NULL) = 0
gettimeofday({1219097455, 105568}, NULL) = 0
gettimeofday({1219097455, 105618}, NULL) = 0
gettimeofday({1219097455, 105659}, NULL) = 0
write(6, "\0", 1)                       = 1
gettimeofday({1219097455, 105828}, NULL) = 0
write(6, "\0", 1)                       = 1
gettimeofday({1219097455, 106294}, NULL) = 0
gettimeofday({1219097455, 106335}, NULL) = 0
select(8, [7], [7], NULL, NULL)         = 1 (out [7])
writev(7, [{";\3\5\0f\0@\4\0\0\0\0\0\0\1\0002\0\30\0008\3\4\0f\0@\4"..., 200}], 1) = 200
read(7, 0x80db96c, 4096)                = -1 EAGAIN (Resource temporarily unavailable)
gettimeofday({1219097455, 106528}, NULL) = 0
select(8, [3 7], NULL, [7], {0, 659131}) = 1 (in [3], left {0, 659131})
gettimeofday({1219097455, 106636}, NULL) = 0
read(3, "\0\0", 4)                      = 2
read(3, 0xbfdca508, 4)                  = -1 EAGAIN (Resource temporarily unavailable)
read(7, 0x80db96c, 4096)                = -1 EAGAIN (Resource temporarily unavailable)
gettimeofday({1219097455, 106770}, NULL) = 0
select(8, [3 7], NULL, [7], {0, 658889}) = 1 (in [7], left {0, 304000})
gettimeofday({1219097455, 465192}, NULL) = 0
select(8, [7], NULL, [], {0, 0})        = 1 (in [7], left {0, 0})
read(7, "\n\3\320\203\37\0@\4\0\320\234\10\1\0\0\0\250\5\304\277"..., 4096) = 32
read(7, 0x80db96c, 4096)                = -1 EAGAIN (Resource temporarily unavailable)
write(6, "\0", 1)                       = 1
write(6, "\0", 1)                       = 1
read(7, 0x80db96c, 4096)                = -1 EAGAIN (Resource temporarily unavailable)
select(8, [7], [7], NULL, NULL)         = 1 (out [7])
writev(7, [{";\3\5\0f\0@\4\0\0\0\0\0\0\1\0002\0\30\0008\3\4\0f\0@\4"..., 4088}, {"\235\6\5\0\372\10@\4\0\0\0\0\0\0\0\0\220\6\32\0", 20}], 2) = 4108
select(8, [7], [7], NULL, NULL)         = 1 (out [7])
writev(7, [{"\235\27\n\0\3\10@\4i\0@\4\372\10@\4\3\1\0\0k\0@\4\n\0\23"..., 104}], 1) = 104
read(7, 0x80db96c, 4096)                = -1 EAGAIN (Resource temporarily unavailable)
gettimeofday({1219097455, 466205}, NULL) = 0
select(8, [3 7], NULL, [7], {0, 299454}) = 1 (in [3], left {0, 299454})
gettimeofday({1219097455, 466279}, NULL) = 0
read(3, "\0\0", 4)                      = 2
read(3, 0xbfdca508, 4)                  = -1 EAGAIN (Resource temporarily unavailable)
read(7, 0x80db96c, 4096)                = -1 EAGAIN (Resource temporarily unavailable)
gettimeofday({1219097455, 466377}, NULL) = 0
select(8, [3 7], NULL, [7], {0, 299282} <unfinished ...>
Process 9832 detached

###### snap ######