without actually having the previous (ME) installation on the drive if you prefer to have the cleanest install possible. Provided you have the CD for the full version of ME, proceed like this:
On a formatted drive, just run the upgrade installer. It will search the drive for a qualifying version and it won't find it, so it will ask you where it is. At that point, take the XP disk out of the CD drive and insert the ME disk. Then point the XP installer to the CD drive. The installer will look at the disk, find the appropriate files, and will then ask you to put the XP CD back in the drive. After that, the installation will continue as normal.