I know this is answered on their FAQ page, but it keeps timing out so I can't link to it.  I've had it running on a PIII-533Mhz w/512 MB, so if you have something like that you should be ok.  Also, it runs best on W2K/WXP or Linux machines.  I don't know that it can't work on W98 machines, but I believe there are problems.