BSOD Help

[Llorrac]

My computer:
AMD Athlon XP 2200, 1.8ghz
DFI AD73 Pro
512mgb Ram
Soundblaster Live
GeForce FX 5500 w/ 256mgb
30gb Maxtor HD
400w power supply
CDRW
DVDrom
Running Windows XP Home

I've been getting BSODs for a while now, at first it just referred to hardware. I just replaced the 300w pws with the 400w, replaced my heatsink with a better one (temp is now around 30c idle and 35c-45c running) and replaced my video card to the one above. I now get 2 different BSODs shown below. Can anyone please tell me what I should do? I have the latest drivers for everything. And when I installed the video card I got a pop-up that said the drivers did not have the Microsoft seal of something or other.
BSOD 1:
Driver_IRQL_NOT_LESS_OR_EQUAL
STOP:0x000000D1 (0X8A5BCF78, 0X00000002, 0X00000000, 0XF8177CD8)
NV4_mini.sys - Address F8177CD8 base at F811B000, datestamp4061D74B
BSOD 2
Stop: 0X000000BE (0XF8481F10, 0X025BA121, 0XF897D5B0, 0X0000000B)
FastFat.sys Address F8481F10 base at F847F000, Datestamp 3d6de58d

What do these mean and what can I do about it?
Thanx

[Panama Red]

Download Memtest86+ and make a boot floppy. Boot to the disk and let if run for at least two full passes and see if your memory has a problem. Here's a link

http://www.memtest.org/

[Llorrac]

I ran Memtest 86+ for a second time (only 2 passes this time) and it found no errors in RAM.
My thoughts are there's something wrong with the NV4_mini.sys file (I believe it is a driver for the Nvidia card) but I cant find a way to fix it. I tried old drivers and new and I still get the same BSOD.

[Panama Red]

Do you have or can you borow another vid card? You'd have to uninstall the current drivers first. That would id or eliminate the vid card.

[Llorrac]

I had a gForce 4 Mx in it when the problems began. If I'm interpreting the BSOD correctly, it's the driver not the card. However it'll all have to wait, I'm leaving for two weeks. Thanks for your help.