have you tried booting the computer from a floppy, try a win98 boot disk and boot with cd rom support... that may get you far enough to get it...
will have what you need if you dont have one
also you may find some information here... use only for legit copys please.
let me know if you need more, i'm still looking for one page... it's funny how you can't find exactly what you're looking for when you need it.
edit** also check your boot settings in bios, and make sure you can boot from cd before you boot from hard drive, you may need to reinstall at this point.
also, if you boot from win98 boot disk, it has a text editor... very old but will still read, load drivers for cd rom (select option to boot with cd support) then change directory to your cd rom with xp cd in. type "dir" and look for a file called serial, serials or something like that on the cd, from dos on the win98 boot disk you can read this file and obtain the cd key from the disk itself.