1) SLI is an NVidia Geforce technology. No AMD/ATI cards will work in an SLI configuration.
2) Crossfire is an AMD/ATI technology. No NVidia cards will work in a Crossfire configuration.
3) An SLI setup is based on two identical Geforce cards. You cannot mix and match two different cards such as the Geforce 6600GT and the 8600GTS
4) A Crossfire setup is based on two similar (not necessarily identical) Radeon cards. Cards that you can set up in a Crossfire Configuration are listed on this chart
5) The motherboard you have is an SLI only motherboard. While you can run a single AMD/ATI graphics card, you cannot run two AMD Radeon cards in Crossfire with your motherboard.
So in answer to your questions:
What i want to know is can i put in a standard PCI-e card in here?
Yes, any single, standard PCI-E graphics card will work with this motherboard.
What will it do for the graphics
That is going to depend on the card you install and what power supply is in your systems. Given you current set-up, I'd say that any modern, mid-level graphics card would out perform your current set up.
Also can i put in another card thqats different that is also SLI as in 1x 6600 GT and 1x GeForce 8600GTS 256MB?
No. Since your board is SLI only, you must use two identical NVidia Geforce cards.
Note: When I say identical cards, I mean the same model number, but not necessarily the same manufacturer. As an example, you could use and EVGA GTX660Ti and an XFX GTX660Ti in an SLI set up.