I'm not sure if anyone's converted the Discworld games to Ipod Touch/Iphone. You could have a look at the independent community: A lot of weird projects go on there.
Alternatively, if you're feeling especially brave, you could seek help on running a Windows or DOS emulator on your handheld. This would almost certainly mean 'jailbreaking' it, doing a bit of hacking and definitely voiding your warranty, but the end result would be that you could run the original Windows/DOS versions of the games, as well as any other touch-friendly computer game from earlier days.
Actually, the Discworld games are pretty much abandonware now, which means that nobody really sells them any more and the only way to get them is to download them from - ahem - certain
sites. So you could get them for your PC without much trouble.
Here we go: