I had an HP 6735s which also came pre-shipped with Vista. While the sticker claims that these machines are 'Vista ready', I found that this is only the case if you literally ran nothing else on it most of the time...
As Techno said, XP will breeze along without a hitch due to it's leaner build. I installed XP on mine as Vista just started chugging along if you opened anything even remotely taxing.
So, yes, I'd highly recommend putting XP on, but if you're thinking of going that route, make sure you're able to get the drivers for it first as XP is notoriously poor at searching for specific drivers. Also be aware that you may need to modify a setting in the BIOS to allow XP to install properly as most HP's of that time were set to load from a SATA configuration but XP lacked these drivers resulting in a boot-loop ('BIOS - System configuration - SATA device mode - select: IDE - Confirm' if this is the case).
If all that seems a bit much (the drivers will be the main problem) and you wish to stick with Vista, the uxtheme patch only changes one byte, modifying the 'install custom themes' option from no, to yes. Other than verifying whether you can apply a certain theme, uxtheme isn't used anywhere else, and won't affect stability in the slightest.
Also, while 7 is the recommended upgrade route, I sincerely doubt that your laptop would be able to run it effectively, if at all.
The final decision, of course, belongs to you...
~ A good choice, I'd be using the same if I could get away with 8GB ram under 32bit. Good Luck! ~