Getting guitar software - like Guitar Rig, Amplitube, ReValver Mk II, or GuitarFX 3 - to work on your machine, you may need a new soundcard with ASIO support (i.e. low latency) with native ASIO drivers.
If you don’t have a audio inteface with ASIO drivers, you could try ASIO4ALL. ASIO4ALL is a universal ASIO driver for WDM audio that wraps ASIO capabilities around your existing sound card. Works for a lot of audio interfaces - but not all. ASIO4ALL is freeware. Asio4All may even surpass native ASIO drivers for some soundcards.
If this doesn’t work, you need a new audio interface.
USB, FireWire or PCMCIA card/PC CardBus (for laptops).