It's not that hard to remove default software installed by vendors like HP.
Obviously, start with the "Add/Remove programs" control panel applet and remove every program with which you aren't familiar.
Then download
Autoruns from Sysinternals. Uncheck everything that was not installed by a company you trust (i.e., Microsoft, your antivirus provider, etc.) This little program is excellent, and it's a good idea to run it periodically after installing your own software. It's englightening to see what type of "auto-startup" crap gets installed by programs like Acrobat Reader.
Personally, I don't like Registry cleanup programs because they have the tendency to make an unnecessary mess of things. Leaving a few extra keys in the registry after software is uninstalled doesn't really harm things much. They're like benign tumors: they don't serve any useful function, but they don't harm anything and cutting them out is more trouble than it's worth sometimes.
The worst thing to have to fix, in my opinion, is that of improperly formatted hard drives. Some vendors ship system partitions formatted with FAT32. This is absolutely ridiculous in this day and age. Fat32 does not have file-level security (no access control lists), and the "convert" program doesn't do a perfect job of re-creating the necessary security tokens when you try to convert to NTFS. At least it's possible. But when faced with this type of system, I typically just wipe and reinstall everything with my own retail Windows CD.