Definitely make copies of your personal files and folders, dtilbury, and put them on an external hard drive (as you mentioned) or you could copy them onto travel drives. In fact, you really should back up all of your data, especially including your SWSETUP folder (which has your Vista preloaded apps and drivers. You may need some of them, others may have been replaced with Win 7 versions on HP's download site for your model, however that said, if they are Vista compatible, they should run in Win 7 with no problems. If any Win 7 app doesn’t work, you can use your backed-up data to bring it back.).
I would think that HP's upgrade disks would NOT be clean and free of HP bloat. gregrocker gave some excellent advice, which I think would be well heeded. Great post gregrocker. Rep + to you!