memory compatibility problem?

Hi,
I have a new computer and am experiencing a number of problems which I would appreciate some help with.
The main problem I think is that the system hangs more often than I would like and each time it hangs it freezes i.e. no amount of Ctrl+Alt+Delete will make any difference. This usually occurs when opening a number of programs whilst surfing the net, two or three perhaps (not so many I would have thought) but it can also happen when listening to streamed midi music whilst. having a number of IE browser windows opened. Without connecting to the internet the system is fairly solid but still occasionally it will hang and on start up I sometimes receive an illegal operation window that displays the information below:

EXPLORER caused an invalid page fault in
module KERNEL32.DLL at 017f:bff87ede.
Registers:
EAX=c00301a8 CS=017f EIP=bff87ede EFLGS=00010206
EBX=0059f940 SS=0187 ESP=0055ffa0 EBP=0056000c
ECX=005601c0 DS=0187 ESI=819227d4 FS=2e8f
EDX=bff76855 ES=0187 EDI=005601e8 GS=0000
Bytes at CS:EIP:
53 56 57 8b 30 83 7d 10 01 8b 4e 38 89 4d f8 75

This is more likely to happen if the prog Messenger 6 is set to open on startup but not necessarily it can happen at times that it isn't (perhaps I should add that windows explorer is not set to be opened on starting Windows)

The operating system installed is Windows98se though I did try to install XP without success at the time being told that the memory that I had bought was not compatible with the CPU or perhaps the memory available was simply not enough.
I run Norton Utilities regularly and there doesn't seem to be any indication of anything seriously being wrong with the discs.
Because I was told by the person I got to fit this system, that I may experience memory problems due to differences in speed between processor and memory I went into the BIOS and made suggested (suggested by the manual) adjustments to enhance compatibility - it may have improved things but it certainly didn't resolve the freezing issue. But since then I've also spotted that the VGA card uses SDRam whilst the Kingston is DDR - could this be the cause I wonder? Anyway any help would be greatly appreciated.
Here is a list of the different components the system is comprised of:

Processor - Pentium 4 2AGHz
System Bus 400MHz, 512KB L2-Cache, PGA-478 Pkg

M/B - ASUS P4S533 - MX , SIS651, FSB533MHz, ATA133 ,

Memory - Kingston DDR PC2700 256MB 333MHz

VGA card - ASUS V7100 PRO 64/PURE - Geforce2MX 400, 64MB SDRam, AGP4X

Seagate 40MB hardrive

DVD ROM (make?)
CDrw dive LITEON
Standard case

maybe you've got faulty RAMs? borrow a stick of RAM from your friends and see if your system runs fine...

can I borrow yours
I ran Memtest and it spotted a legion of errors so I reseated the stick in another slot ran the prog again and got similar results

Thanks for the tip

heh consult your motherboard manafactuer.