you can merge to partitions on a single disk, although this should be one of your last resorts. when two partitions are created on a single drive the OS recognizes the two partitions as two seperate drives. From win xp pro, you can access all the data on the partition with xp home platform. the second partition will take up close to a gig of space that could be used. the simplest way would be to creat shortcuts to the programs you want in the partition for xp pro. then right click my computer> properties> advanced> start up and recovery settings> select win xp as the default OS and deselect the box marked "time to display operating systems"
this will stop that annoying 30 sec pause that you get when you start your computer asking which OS you want to run.
or if you seriously want to merge the two, here is a link with a download that will help.....download this file and creat an disk to insert into the disk drive and restart to load from the disk
the only thing is that if you write over or delete files that those programs need to run smoothly, you will have to reinstall them completely. in which case you would be just as well off to back up your info and do a clean install. i trust you will be able to determin which solution is best for you needs.
Personally if i had programs i wanted to save, i would take the first option and just have two partitions