Hiya! if the disc is a RETAIL version you may be in luck! a retail version can go on many pc's! for example ive had a xp pro Retail disc (Genuine) for around 5 years! in that time ive formatted (Low level format) and placed it on around 45 pcs! & NONE of them came back to me!
now a days if your after XP or Vista you can buy them for dirt! around £40 for XP & around £50-70 for vista (Pending on what type as in premium/home/ultimate)
I forgot to check how old the thread is so i may be way too late..Anyway if it helps it was worth it..