Mini card? You mean a low profile card? In which case yes, you just need to pick one that is small enough to fit in your case and has a low profile plate included. You need to look at the Motherboard specs of your PC and see if it has a PCI-E x16 slot and check to see if it is available.
If it is really really old it may need an AGP or PCI video card. IF it is PCI-Express then something like this will work, but I don't know what your goals are as far as performance. http://www.newegg.com/Product/Product.aspx?Item=N82E16814102882