it may be trying to find a driver for a certain app and having trouble loading it, when you first got the laptop it booted fine until you reinstalled XP home did you have a recovery disc or the full xp stand alone disc?
by the way have you checked for spyware? and virus?
run
http://www.lavasoft.de/support/download/ download from that link...
when you reinstalled xp were you able to use the generic drivers provided with it and have you stook with them?
NAV is a resource hog and if you want to do an online virus check you can go here
http://housecall.trendmicro.com/ it is a good online free service...
also black viper gives a lot of great tips for configuering xp home
http://www.blackviper.com/WinXP/servicecfg.htm
I have never owned a laptop or messed with one...
also goto run type msconfig goto start up and disable everything from startup apart from what you need..see if boot up is better if so go back and switch one back on for start up and keep doing that until you find which app is causing the slow boot up...