Hello valmontgtx, welcome to Seven Forums!
Don't delete the entry in msconfig first, do this wipe and resize first and the enrty will be removed all by its self.
The boot files are on XP so removing Vista will cause no issues at all.
The best way to do it is to do a partition specific wipe "secure erase" to the Vista partition first as that will over-write any windows code and anything else that could cause issues when you extend into that partition; just be sure to backup anything on the partition first as once over-written the data will go gone for good.
Have a look at Option Three in this tutorial at the link below to see an out-line on the wipe process; also have a look at Option Four of the same tutorial if you want/need to convert the logical into a primary.
Be sure to post back with any further questions you may have and to keep us informed. Partition Wizard : Use the Bootable CD