Bad Memory?

hey folks,
i've had minor stability issues since i built my e6600 setup a couple years ago, these issues seem to be quickly exaggerated when attempting even modest oc'ing. i'm wondering if it looks like bad memory to you? thanks in advance for any help ...

setup:
e6600 2.4 @ 2.6MHz (289x9) 1.2V, MSI P965 Platinum (up to date BIOS), corsair xms2 ddr2-800 (week 23 of 06), XP sp2. i've knocked the DRAM down to 667 for a FSB/DRAM of 4:5 (vs 2:3 on auto), and it seems very slightly more stable. i believe the multiplier is fixed at 9 with this board/cpu combination. stock air cooled, temps at load are well below 50C at all of these settings, i've tried adding up to 0.0500V to the CPU with no improvements in stability so i've returned it to stock VID. the primary use of this machine is hd video editing.

behavior:
from stock to 2.6/7MHz: mostly stable, after using dvd drive multiple times system often fails to launch new applications (does nothing, only previously open apps are functional), wont restart through os, have to force. occasionally it becomes sluggish over time and needs to be restarted. very rarely system will restart at random.
at 2.8MHz: prime95 blend will eventually error, restarts are more regular at full load
at 3.0MHz: windows will not boot

memtest86:
says 5 errors, also says fails test #7 with 56 errors, 122 err confidence, lowest address 0MB, highest address 4095MB

i'm definitely no expert but i think this machine should be able to run stable at 3 to 3.2 with stock cooling, as i've had no temperature issues.

thanks again for any help, let me know if there's additional info i can provide or if there's something i should test.
cheers

Memtest errors almost guarantee BAD RAM.

You likely have a lifetime Warranty on your RAM.

If you have more than one stick, try running one at a time and test each with Memtest.

RMA your RAM.

If you RMA, consider getting a little more RAM just to have some before you do so. I assume you have a 32-bit system which can handle about 3GB of RAM. In this case, if you have 2GB (2x1GB) get another 1GB (2x512MB). I'm also assuming you have 4 slots. If you only have two slots it makes it harder as you'd have to either go without RAM while you RMA or buy some and sell your returned RAM.