The macros could be stored in a number of places, either in your personal.xls file which would be in your XLSTART folder, or in each individual file that uses them.Use the XP Search wizard to see if you can find a personal.xls file in a path something like this:
C:\Documents and Settings\user_name\Application Data\Microsoft\Excel\XLSTART
If you have a personal.xls file, rename it and move it to another (safe) location so you can put it back later. If a personal.xls file exists in the XLSTART folder, then the macros in that workbook (which is usually hidden) are available to every workbook whenever Excel is open.
You could try going to Window…Unhide in Excel and see if you see a hidden personal.xls listed there.
If you don’t have a personal.xls file in your XLSTART folder, then the macros are probably stored in the VBA modules of the specific workbooks you use them in. I doubt a reinstall would impact those files, but I’d back them all up just to be safe.
The .xlb file should be in folder one level above the XLSTART folder, but I can't say for sure. Use the XP Search wizard to look for it. Search for *.xlb since the first part of the filename will be dependent on the version of Excel you are running.
Keep in mind that there are a vast number of different configurations of XP machines, so it’s hard to say definitively where everything is. On my corporate-imaged machine there are actually *two* XLSTART folders, and Excel looks at both of them when starting up, but will only use the personal.xls from one of them. Very strange.