Operation system half installed ???

Wondering if anyone can help ... i have xp home halfway downloaded but noticed i don't have a product code. Now that i found my xp professional and windows 98 with codes i don't know how to put them in because it keeps booting into xp home and won't let me proceed. I've tried everything and am going crazy because it's been four days and haven't been able to get any further along. Before you say take it in .... i'm a single mom and don't have money for that at this point and need my home computer for the kids ... so any help would be greatly appreciated.

Jenn