Problems only when starting up

First the specs:
AMD Athlon 64 3700+ San Diego
DFI LanParty UT NF4 Ultra-D with 310 BIOS
2x512MB Crucial PC3200 RAM in the orange slots
ATI Radeon X800XL 256MB PCI-Express
Chaintech AV-710 sound card
Windows XP Pro SP2
Fortron Blue Storm 500W PSU
Latest drivers AFAIK

Nothing is overclocked or has even been overclocked yet.

I've been having some strange problems on my new rig. The only problems that occur, happen at startup, everything else is fine. It has been folding for 2 weeks and has not crashed once in games or doing anything, the only time I have problems is on the startup.

Sometimes I get errors, sometimes I don't, it's very strange. The errors are anything from an "Entry Point Not Found" when something tries to access a DLL on startup, to the Spooler service not starting, to svchost.exe errors (event 1003 according to the Event Log). About 3 times on startup (out of 100+ startups), I have got a BSOD that says "DRIVER_IRQL_NOT_LESS_OR_EQUAL". I have some screenshots that I can post if needed.

I've been in the BIOS trying to find the problem, I've disabled stuff I don't use, as well as messed with some other stuff. The problem doesn't seem to be tied to a certain device or a certain driver so I just don't know what to do.

I guess what I am trying to find out is if it sounds like my Windows Install has somehow gone bad and I need to re-install, or if it is a hardware, BIOS, or driver problem. Any input is appreciated, I'm about to pull my hair out over this

www.memtest86.com
Start with testing your memory. 90% of bad installs are memory related.

Yeah I ran Memtest for about 12 hours last night, no problems. Should I run it longer?
I have have changed a lot of BIOS settings since I installed Windows. Do you think it is possible that I had something set bad during the install that may have caused these problems?

UPDATE:
I have been working on it for the past few hours, I have changed some BIOS settings, and also defragmented the hard drive. I have had almost no startup errors recently (say in the last 30 restarts), but I have had 3 "CMOS Checksum errors - Defaults Loaded". I think I solved one problem and another comes up?!?

I am still restarting and seeing if I get more errors, keep the input coming.

Wow, I can't believe it

I went ahead with a clean install, everything seemed to be going fine, I had no errors for 2 days (I restarted about 70 times), then I started getting errors today. It wasn't just after I had added some hardware or software either, I have been restarting a lot and it restarted over 75 times without a problem, now I have had 2 or 3 errors in the past few restarts. What could be going on?

are they cmos errors if so try replacing the mobo battery or give me the whole system and buy your self a newer better one

Why not just load up the fail safe defaults and see what happens. The BIOS can be overwhelming and this is an easy way to rule out settings being a source of the problem.

After that I think I would try a PCI (non-express) card. If thats good then try the X800XL with a different driver version. Check to make sure the card is not sharing an IRQ with anything, and get the latest drivers for everything while your at it.