Am using a clean install of kubuntu 7.04 (today) (June 4th 2007), after a year of 6.06 kubuntu with no problems. Suddenly today, several freezes. Only firefox has been installed aferr full new install and updates. (firefox is not being used wwhen freezes have occurred). 
Wired ethernet only, 

The only unusual thing I can I note about this machine today is - when running apparently ok, and ctrl alt backspace used (as a test) then the xserver does not re start and offer a new login, although I can then use crtl F1 to get terminal and shutdown.

lsmod as follows (hth)

user@dabs1:~$ lsmod
Module                  Size  Used by
rfcomm                 40856  0
l2cap                  25728  5 rfcomm
bluetooth              55908  4 rfcomm,l2cap
ppdev                  10116  0
speedstep_lib           6148  0
cpufreq_stats           7360  0
cpufreq_userspace       5408  0
cpufreq_conservative     8200  0
cpufreq_powersave       2688  0
cpufreq_ondemand        9228  0
freq_table              5792  2 cpufreq_stats,cpufreq_ondemand
tc1100_wmi              8068  0
dev_acpi               12292  0
pcc_acpi               13184  0
sony_acpi               6284  0
battery                10756  0
ac                      6020  0
button                  8720  0
video                  16388  0
sbs                    15652  0
container               5248  0
dock                   10268  0
asus_acpi              17308  0
i2c_ec                  6016  1 sbs
backlight               7040  1 asus_acpi
ext2                   66824  1
reiserfs              247680  3
ipv6                  268960  8
lp                     12452  0
fuse                   46612  0
snd_intel8x0           34332  4
snd_ac97_codec         98464  1 snd_intel8x0
ac97_bus                3200  1 snd_ac97_codec
snd_pcm_oss            44544  0
snd_mixer_oss          17408  1 snd_pcm_oss
snd_pcm                79876  4 snd_intel8x0,snd_ac97_codec,snd_pcm_oss
snd_seq_dummy           4740  0
snd_seq_oss            32896  0
snd_seq_midi            9600  0
snd_rawmidi            25472  1 snd_seq_midi
snd_seq_midi_event      8448  2 snd_seq_oss,snd_seq_midi
parport_pc             36388  1
parport                36936  3 ppdev,lp,parport_pc
snd_seq                52592  6 snd_seq_dummy,snd_seq_oss,snd_seq_midi,snd_seq_m
idi_event
snd_timer              23684  3 snd_pcm,snd_seq
snd_seq_device          9100  5 snd_seq_dummy,snd_seq_oss,snd_seq_midi,snd_rawmi
di,snd_seq
serio_raw               7940  0
iTCO_wdt               11812  0
iTCO_vendor_support     4868  1 iTCO_wdt
i2c_i810                6276  0
pcspkr                  4224  0
psmouse                38920  0
i2c_algo_bit            8712  1 i2c_i810
snd                    54020  16 snd_intel8x0,snd_ac97_codec,snd_pcm_oss,snd_mix
er_oss,snd_pcm,snd_seq_oss,snd_rawmidi,snd_seq,snd_timer,snd_seq_device
soundcore               8672  1 snd
snd_page_alloc         10888  2 snd_intel8x0,snd_pcm
intel_agp              25244  1
agpgart                35400  1 intel_agp
i2c_core               22656  3 i2c_ec,i2c_i810,i2c_algo_bit
shpchp                 34324  0
pci_hotplug            32576  1 shpchp
af_packet              23816  4
tsdev                   8768  0
evdev                  11008  3
ext3                  133128  1
jbd                    59816  1 ext3
mbcache                 9604  2 ext2,ext3
ide_cd                 32672  0
cdrom                  37664  1 ide_cd
ide_disk               17024  9
ata_generic             9092  0
libata                125720  1 ata_generic
scsi_mod              142348  1 libata
generic                 5124  0 [permanent]
usbhid                 26592  0
hid                    27392  1 usbhid
8139cp                 25088  0
floppy                 59524  0
piix                   11140  0 [permanent]
8139too                27648  0
e100                   36232  0
mii                     6528  3 8139cp,8139too,e100
ehci_hcd               34188  0
uhci_hcd               25360  0
usbcore               134280  4 usbhid,ehci_hcd,uhci_hcd
thermal                14856  0
processor              31048  1 thermal
fan                     5636  0
fbcon                  42656  0
tileblit                3584  1 fbcon
font                    9216  1 fbcon
bitblit                 6912  1 fbcon
softcursor              3200  1 bitblit
vesafb                  9220  0
capability              5896  0
commoncap               8192  1 capability
user@dabs1:~$