|Depends! Is it also slow to use once running?|
Most common causes of slow startup are too many programs starting when windows does (couple with a lack or RAM - should have at least 512MB RAM for XP to run ok, nowadays, more is better) or windows having problems loading drivers/starting services (because of corrupt/bad driver or system files). Try starting in safe mode (tap F8 key before windows starts to get the menu) - if that starts in reasonable time, then it is one of the above. You can edit the startup list using msconfig (built in xp - start, run, type msconfig in box, ok it, look at the startup tab) or something like autoruns (google to find). Basically only program that need to be starting with windows is internet security - everything else you can start when you need them. If you prune this list and still slow, then probably driver load issue - more difficult to sort (better using a professional) - though a repair reinstall might do the job (if you have an xp install disc for your installation).