Probably not. In my experience, CDs of a similar type can use the serial number of the same type with no problems. For instance, WinXP Home, UK version, with SP1, Full retail, will work with anothers serial number of the same configuration.
BUT - change that to non-UK version, or OEM version, or non SP1 version, and it won't work.
All the combinations I've tried abide by the above rules, but clearly I haven't tried all combinations by a long way.
There are two repair options in XP (as there is in 2000) - if you choose the first 'R' then you are asked for the password, which unless you have set one, as Powerless has said press enter. This brings to a command prompt and you then use console commands to do various repairs. If instead of pressing 'R' you continue as iif you were doing a new install you will then get a secong option to select 'R'. This will then do an automated repair (which is a bit like a full reinstall). This does not change any of the file system etc but you will have to reinstall any Windows service packs. This is why you should be able to use a full up XP disk rather than your computer restore disc as long as you use your own Id key.