WHOA - B4 running out & dropping cash on a new drive, first run some diagnostics on you drive (HDTune or Hitachi's DFT) and run a memory test (Microsoft's Memory Tester or Memtest32) to make sure this is actually hardware related...all of these apps can be downloaded from MajorGeeks.com or a similar site....
You may not even have a hardware problem...you could have a startup application that's slowing down your boot...run "msconfig" in XP to take a peek at what's loading at boot time...