which processor to buy???

For 15k to 20k you should go for amd cpu - phenom X4 940BE - around 11k
asus M3A-H -around 7.5k if you are able to get a good deal on 790GX or 790FX then go for it.

With the remaining budget buy ram.
Increase ram to 3gb or 4gb(if you will run 64 bit os)
P.s. - you should have posted this in q&a section and not in reviews

Phenom II X3 720 B.E. 2.8GHz @ 7.8k
2*2GB Kingston DDR2 800MHz @ 2k
Biostar TA790GXB 128M (790GX + SB750) @ 5.8k

Total = 15.6k

Seriously, don't spend more cuz u hav an 8800GT.

Instead of that biostar mobo, Jetway HA 07 Ultra is much better with lot better PCB and capacitors.

^^^The temps of the voltage regulators in the Jetway mobo reaches an uncomfortable and extremely high 80C.

i had amdx2 4200+,

Click to expand...

But thats not a bad proccessor atall. IMHO there is no need to upgrade your processor.

^ thats right actually.. he better upgrade when the newly announced processors are available.

An advice to the OP: You have a decent enough rig right now. Stick with it till around September when new AMD CPUs launch. Why do you want to hastily upgrade now when the Budget/VFM range products in AMD 45nm K10.5 "Stars" architecture have not even appeared in the market till now ?

If you look at MY configuration, Pentium 4 2.66GHz, Intel D915GLVG mobo with GMA 900 graphics, 1GB Hynix DDR 400MHz RAM, 80GB HDD and a horrible keyboard/mouse/speakers/monitor/UPS/case to back these up, you might think I'm getting an upgrade tomorrow. But even I have decided to wait till around September since I can carry on with this rig for some more time.

^^ Thats too horrible to even read, and u want to wait 100 more days ???

u r the limit !!