Ubuntu 10.04 Randomly Freezes

I am a newbie attempting to figure out why Ubuntu 10.04 keeps freezing (i.e. no keyboard or mouse input and screen is locked).

I'm using the following system

Ubuntu 10.04 (lucid)
Kernel Linux 2.6.38-15-generic
GNOME 2.30.2

Hardware
Memory: 2.0 GiB
Processor: AMD Athlon XP 2800+
Available Disk Space: 404 GiB
Soundcard: Xonar DS (Asus) *PCI)
Video: Matrox G450 (PCI)

Symptom: This box has never run more than a week at most (sometimes a day) without freezing.

here's a look at the final lines of syslog just before each crash/freeze:
------------

Jul 18 15:35:32 fsr1 avahi-daemon[440]: New relevant interface eth0.IPv4 for mDNS.
Jul 18 15:35:32 fsr1 avahi-daemon[440]: Registering new address record for 192.168.1.125 on eth0.IPv4.
Jul 18 15:35:32 fsr1 dhclient: bound to 192.168.1.125 -- renewal in 41837 seconds.
Jul 18 15:35:32 fsr1 gdm-session-worker[1239]: GLib-GObject-CRITICAL: g_value_get_boolean: assertion `G_VALUE_HOLDS_BOOLEAN (value)' failed
Jul 18 15:35:33 fsr1 NetworkManager: <info> (eth0): device state change: 7 -> 8 (reason 0)
Jul 18 15:35:33 fsr1 NetworkManager: <info> Policy set 'Auto eth0' (eth0) as default for routing and DNS.
Jul 18 15:35:33 fsr1 NetworkManager: <info> Activation (eth0) successful, device activated.
Jul 18 15:35:33 fsr1 NetworkManager: <info> Activation (eth0) Stage 5 of 5 (IP Configure Commit) complete.
Jul 18 15:35:33 fsr1 gnome-session[1259]: WARNING: Could not launch application 'bluetooth-applet.desktop': Unable to start application: Failed to execute child process "bluetooth-applet" (No such file or directory)
Jul 18 15:35:33 fsr1 ntpd[810]: ntpd exiting on signal 15
Jul 18 15:35:33 fsr1 ntpd_initres[830]: parent died before we finished, exiting
Jul 18 15:35:34 fsr1 polkitd[1435]: started daemon version 0.96 using authority implementation `local' version `0.96'
Jul 18 15:35:34 fsr1 ntpdate[1415]: adjust time server 91.189.94.4 offset -0.111763 sec
Jul 18 15:35:34 fsr1 ntpd[1472]: ntpd 4.2.4p8@1.1612-o Tue Apr 19 07:08:29 UTC 2011 (1)
Jul 18 15:35:34 fsr1 ntpd[1478]: precision = 1.000 usec
Jul 18 15:35:34 fsr1 ntpd[1478]: ntp_io: estimated max descriptors: 1024, initial socket boundary: 16
Jul 18 15:35:34 fsr1 ntpd[1478]: Listening on interface #0 wildcard, 0.0.0.0#123 Disabled
Jul 18 15:35:34 fsr1 ntpd[1478]: Listening on interface #1 wildcard, ::#123 Disabled
Jul 18 15:35:34 fsr1 ntpd[1478]: Listening on interface #2 lo, 127.0.0.1#123 Enabled
Jul 18 15:35:34 fsr1 ntpd[1478]: Listening on interface #3 eth0, 192.168.1.125#123 Enabled
Jul 18 15:35:34 fsr1 ntpd[1478]: Listening on interface #4 lo, ::1#123 Enabled
Jul 18 15:35:34 fsr1 ntpd[1478]: Listening on interface #5 eth0, fe80::20c:6eff:fee5:610d#123 Enabled
Jul 18 15:35:34 fsr1 ntpd[1478]: kernel time sync status 2040
Jul 18 15:35:34 fsr1 ntpd[1478]: frequency initialized -14.735 PPM from /var/lib/ntp/ntp.drift
Jul 18 15:35:34 fsr1 anacron[1512]: Anacron 2.3 started on 2012-07-18
Jul 18 15:35:34 fsr1 anacron[1512]: Normal exit (0 jobs run)
Jul 18 15:35:35 fsr1 nautilus: [N-A] Nautilus-Actions Tracker 2.30.2 initializing...
Jul 18 15:35:35 fsr1 nautilus: [N-A] Nautilus-Actions Menu Extender 2.30.2 initializing...
Jul 18 15:35:36 fsr1 acpid: client connected from 1621[108:114]
Jul 18 15:35:36 fsr1 acpid: 1 client rule loaded
Jul 18 15:35:39 fsr1 kernel: [ 31.360020] eth0: no IPv6 routers present
Jul 18 15:35:48 fsr1 gnome-session[1259]: WARNING: Could not launch application 'gnome-user-share.desktop': Unable to start application: Failed to execute child process "/usr/lib/gnome-user-share/gnome-user-share" (No such file or directory)
Jul 18 15:36:03 fsr1 gnome-session[1259]: WARNING: Could not launch application 'evolution-alarm-notify.desktop': Unable to start application: Failed to execute child process "/usr/lib/evolution/2.28/evolution-alarm-notify" (No such file or directory)
Jul 18 15:36:30 fsr1 kernel: [ 82.777350] ondemand governor failed, too long transition latency of HW, fallback to performance governor
Jul 18 15:36:37 fsr1 AptDaemon: INFO: Initializing daemon
Jul 18 15:39:55 fsr1 ntpd[1478]: synchronized to 91.189.94.4, stratum 2
Jul 18 15:39:55 fsr1 ntpd[1478]: kernel time sync status change 2001
Jul 18 15:41:38 fsr1 AptDaemon: INFO: Quiting due to inactivity
Jul 18 15:41:38 fsr1 AptDaemon: INFO: Shutdown was requested
Jul 18 16:17:01 fsr1 CRON[1775]: (root) CMD ( cd / && run-parts --report /etc/cron.hourly)
-----------------------------------------
Any clues?

Thanks a great deal in advance!

Steve