I came accross this website recently as a link from an italian slot car racing club and its great fun for anyone who used to enjoy scalextric.
http://www.tv4.se/lattjo/kojan/bilbanan.asp
Simply put it allows you to build and race on a virtual scalextric track against the computor or your mate (if you have one
)Its free of adware etc and can become compulsive, I almost got out my remaining scalextric stuff!
Check it out and report back