I am thinking of buying the gtx 295 but i have herd that some games like gta4 and other do not support ither sli or dual core graphic cards is that so and if so are there many other games that do not support sli or multi core?
You will not have a problem with finding games to support SLI.
Only quite old games will be without support, or any DX9 game run in windowed mode.
Your configuration already shows that you have a gtx285.. A 295 is not much of an upgrade. Really a waste of money frankly. For far less you could get another 285 for SLI that would spank the 295 in everything. Or you can just wait a couple months for the next generation of cards. The 285 is more than enough to tide you over till there are much much more powerful options.