No - there's no difference
You always have to contact MS to activate XP (it can do it automatically when you have your Internet connection set up. You get 30 days to do it in.
The XP setup routine (boot from the CD - allows you to partition and format your HDD as you wish. You must choose FAT32 or NTFS when you do this - see quirks.
You can do a lan between XP and Win98 - it's very easy.
You can share the connection through the lan - the lan setup does this for you.
Quirks - It works fine - though it's a bit different. When you set up you have to choose the file system - NTFS (best) or FAT32 (for the few things that don't work with NTFS). If you choose FAT32, XP itself will not format a partition larger than 32GB - though it can use one, if you format it another way.