i would give 30€ for it... its a pwnge thing and should have no problems doing some calculations or anything. Thats a perfect system i guess... (Whats an internet card? Do you mean ethernet?)
Oh and are you sure that book even supports 512mb? i doubt you can switch the hdd easily btw
Instead of that, i would think about a decent os (Fedora or Win98, maybe XP) and an external Graphic card...