It is possible. I usually set more than 1 partition when installing but in this instance I would suggest Partition Magic. As long as the HDD is large enough that your new 30G partition will not choke XP.
Run defrag before creating.
http://www.partitionmagic.com/partitionmagic/
Accroding to the prod specs it should be no problem. I myself have never used it.
I am sure the trial will be all you need though. Unless you intend to make a habit of changing the partitions around.