How good your pc need to be to use this program to record gameplay videos without lagging?
My frame rates drop to 1-5 fps when i started to record. i have:

Acer 5920G, Core 2 duo 2.0 (4mb L2 Cache), 2gb ddr2 ram, Nvidia 8600m GT (driver 163.44)

(especially when it's the same version number, as there wouldn't be any incompatablities to deal with).

G013M

I don't quite get what you mean here.

I think i will grap a Nvidia 8600 GTS. OR if 2900XT really could be supported, i might consider that one.
My PC only has basic hardwares which are:

intel D965LT mobo
1 gb 533 ddr2 ram
80GB hdd ( another 250GB external/portable hdd)
a CD rom ( i use external/portable dvd rom )
Asus X1659 pro 256mb ddr2
450 watt power supply

That's all i got in my cpu.. I will only come to the budget part when i know which cards can fix in :) and i think cards sold in my country are expensive.