Vista blue screen error

Hey guys.
I've have some blue screens on my computer for the past year or so, nothing new installed on the computer.
However they used to go away and I'd only get them once every month or so.
Only recently (past couple of days) has this become more + more.
Right now my computer only turns on 1/4 times w/o bsod.
I haven't (to my knowledge) installed anything new on my computer recently.

Anyway, my system -
Windows Vista x32 (with SP1 installed) - not installing sp1 was after all these blue screen errors, so it didn't fix/harm it.
AMD Athlon 64 x2 Dual Core Processor 4600+
2048 mb ddr2 ram
Nvidia GeForce 7600 GS
320 GB hard drive

The errors I have been getting are the following -

IRQL_NOT_LESS_OR_EQUAL (stop: 0x0000000A)
DRIVER_IRQL_NOT_LESS_OR_EQUAL (stop: 0x000000D1)
MEMORY_MANAGEMENT (stop: 0x000001A)
+ also (stop: 0x0000007E)

I was just wondering if somebody could give me some insight into *** is wrong with my computer + if it can be fixed/methods to fix it.

Thanks