Can i put tires currently mounted on a 17 X 7.5 wheel on an 17 X 8 wheel?  

should be fine as long as the tires are big enough to get the bead on the rim  

What are the dimensions of the tire. The wheel size is no issue. 17" on a 17" swap. The dimensions will matter, though. It may make the assembly higher, over all, and cause some performance issues. The width is no issue either. The tire will conform depending if it's not too much conformity that it will need. In short... what size tire are you working with? I know it's a 17" fit but the rest is a mistery.  

i dont know when it comes to tires(most important part of the cars performance and safety) id get tires the right size (not a tire guy so other posts may be helpful im more KONI AND BREMBO)  

like what i said and to simplify what s12rapido3 said whats the tire width?  

I hope this isn't another topic starter...
If you feel that it's too big a width for yor car there's always spacers.
To get the right size spacer you would need a straight edge that will fit the outer most edge of the inner portion of the wheel, edge to edge. Then with another measuring device measure the distance from the part that touches the hub flange to the straight edge. Do the same for the stock wheel and then you do a little math to get the difference between the two measurements. That difference would be the size of the spacer you would need.
I did it for my brothers ZX2 when he purchased my 16"x7.5" wheels and I got a 5mm (a little over a 1/4") difference. I put them on with the spacer and it fit perfectly in the wheel well. Some cars will have the quarter panel well seam rolled but in the end it won't damage any thing and the tire doesn't touch a thing when driving over bumps or going over curbs.