Dude there will be a difference but not much....only in benchmarks will you be able to notice a difference.
I don't understand why would you want to invest in a dual core that too on a dead socket like LGA 775. I understand your budget, but then why don't you save up and wait for some more time, so you can buy a good processor. i mean today you will get a new processor with an old socket but then later(1-2 years) you will have to buy a new quad/dual-core processor WITH A NEW MOTHERBOARD if you want to enjoy games as before because in some years from now all the games will utilise all 4 cores(some years is an overstatment).
But if you want it now, listen to keiki646 and go for a C2D E6300, bte have a llok at this (http://cgi.ebay.ph/Intel-Core-2-Duo-Processor-E7500-2-93GHz-1066MHz-3M-OEM_W0QQitemZ190372880993QQcmdZViewItemQQptZCPUs?hash=item2c531ba261#ht_500wt_956) buy it from here if you trust the seller.
Well my suggestion will be to WAIT !! and invest in a AM2+ motherboard and get an AM3 processor they are backward compatible, you need not buy the expensive DDR3 RAM......GOOD LUCK