http://software.palminfocenter.com/product.asp?id=1047
The amount of freeware for PocketPC is so huge, you can not oversee it entirly. Sometimes when you search for such a game or software with "basic" features or which is a clone, you'll find commercial software first and then when digging deeper, you'll find the same clone from a different author and it's freeware.
If you search for a good overlook on commercial games, check this page here:
Clickgamer.com.
About emulators... it's the same as when you try to run one on a PC ^^
Specific emulator and ROM/Image are often all you need to get a(ny) game started that is in the circle of possibility (means, it should be realistc to perform it).
If you want to have an overlook on the systems you can simulate on your PDA, check the animated image in my signature, I did a page on that =)