|Someone just gave me an XPS T450 recently so I'm somewhat familiar. The system can handle up to 768MB of PC100 (3 x 256MB)...if you don't have at least 512MB RAM, I don't recommend installing XP. I tried it with 384MB & was very disappointed with the performance. I ended up wiping the HDD & going with a lightweight Linux distro. It runs reasonably well, not great, but much better than XP.|
Anyhow, if you insist on installing XP, change your boot order to floppy, CD-ROM, HDD. Boot off the XP CD, wipe out the current partitions, then create one or more new ones. Format as NTFS (I suggest "full" rather than "quick"), then continue with the installation.
You do NOT need DOS, you do NOT need boot floppies. Everything is done with the XP CD, but you MUST have the boot order correct.