Firstly a better description for a title would be best the next time you post.
I'll try to help but this is not a simple problem, let me explain why.
Firstly your laptop. I presume it came with a Windows XP restore disk and not a full XP disk. You may find that there is a hidden partition on your hard drive that has windows XP and all the drivers you need for your laptop.
A hidden partition is basically a part of your hard drive which you cannot see and windows may well be installed in there.
If you blank the computer which you will need to do you will probably lose XP and have no way of putting it back as the info on your hard drive will be gone.
Regarding the FAT32 thing. I believe that Vista uses a new file system and that you would need to format (that is blank) the computer with this new file system, which you should be able to do from the Vista disk and then install Vista.
But heres the problems. If you did this then you lose XP totally. Theres no way to get it back. You might have to buy another copy of XP if the Vista installation failed. Also 64 bit Vista uses different drivers than the more common 32 bit Vista. Now the Vista disk MIGHT have many of the necessary drivers on the disk, but it might not. If it doesn't then you would need to get them from the HP website. But there might not be 64 bit drivers written for your laptop and you need 64 bit Vista drivers, 64 bit XP ones will not work. You can see the problems. If you can't get these drivers then at best your computer might work but not too well and it worst it would either crash or just not run.
I've had a look and there do appear to be 2 64 bit Vista drivers, here they are click here
but I have no way of knowing whether these are all you need, perhaps the other drivers are built into Vista but I just don't know, if any drivers are missing then it just won't work properly.