I think the assembler of ur friend is acting smart.

Assemblers purposely ask use to not use partition tools, tweaking tools, performance boosing tolls and say that it will be harmful for the system. But believe me the sole reason for that is if by chance you mess up (crash the OS) with the system, he is the one who has to come to repair it, as it is under onsite warranty.
It ur friend's onsite warranty is over, then i think the assembler is a real dumb guy to say that. The only problem with partitioning softwares is that, you have to do it carefully and resizing partitions are very time consuming. U can use s/w like PArtition magic, Acronis Partition Expert, Ranish PArtition manager etc. which r very good ones.
While formating a new hard disk..... u can create the primary partiton while installin Windows Xp itself. Once install, go to Disk manager and create the rest partitions. Use quick format.