First of all what is your current configuration ?
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20-25k is a bit low for core i7 system, and somewhat even for i5.
i5 retails at 11k (just the processor alone)
i7 920 retails at 16k
Appropriate motherboard for either i5 or i7 from 15k - 22k. (ASYS, Gigabyte EVGA)
(cheaper ones havent arrived yet)
DDR3 RAM is a bit expensive right now so minimum 2GB = 2.5k
A better power supply for the new system = 4.2k (at least a 450W SMPS)
( depends what kind of power supply [SMPS] you have right now)
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Alternatively AMD config
Processor, take your pick
AMD Athlon II X4 620 (2.6Ghz) Quadcore = 5,400/-
AMD Phenom II X2 550BE = 5.3k
AMD Phenom II X3 720 BE = 7.3k
AMD Phenom II X4 955 AM3 = 12k
Motherboard
ASUS
M4A785TD-V EVO (785G) = 7.5k
Crosshair-III-F = 14.3k
Gigabyte
GA-MA785GM-US2H (790G) = 4.5k
GA-MA790X-UD4P = 10k
Throw in some DDR3 RAM which should be in a kit (2x2GB, 3x2GB kits) from Corsair, OCZ, Kingston, G.Skill etc

= 7k
spend like this
5-7k for proccy
7-10k for motherboard
3-7k for RAM
= 24k.. at most.
4k at least for powersupply

(optional, if you already have a certified 450W or greater PSU )
= 28k
I'd say buy a AM3 socket motherboard with high end config and features (with either the 790 or 785 Chipset),
Go for the Tri Core Phenom or baseline AMD Athlon X4 620 or Phenom X2 550BE (which could be unlocked to four cores) and wait for a better processor to come from AMD. At least AMD based motherboards remain upgradable for a longer time than intel based ones
Core i5 may be better than all the processors above, but also you'll be stuck with it if intel plans to change sockets again

..