U can do try out this setting:
SInce ur mobo is a p4, im guessing its a bit older like say 1.5 to 2 yrs old.
SO a DDR1 RAM will be supported, if ur mobo is of the Model: D845 or D865 series, u can go in for a DDR1 RAM of upto 400Mhz speed, i mean this way...
512 MB DDR1(400) x 2 modules, so that u can have 2 RAMs in the 2 slots (this can be the MAX no, of RAM slots even if u hv a PC thats old) and use the 2 RAMs in DUAL CHANNEL mode..
Remember: Both the RAMs shud be of same company and SAME Speed (the Mhz part) else there will be compatibility issue.
A transcend 512 MB DDR-1 400 Mhz RAM will cost u approx. Rs.1200/- while
A Zion RAM of the same config will be about Rs.850/-
NOTE: U can type dxdiag in the RUN box (Start>Run) and see the type of motherboard that u are having, then search for the manual on net (if u hv lost one, that is

) and see upto wat speed is supported by ur mobo for the RAM and buy accordingly..
Cheers n e-peace...
Cheers n e-peace....