As far as I know, the only trial version of XP available is the 64-bit edition which requires a 64-bit AMD Opteron– or Athlon 64-based computer. (
Click Here for all the system requirements.
If you're not sure whether your copy has been activated, if you go to Start>All Programs>Accessories>System Tools there should be an "Activate Windows" entry. Click on that and it will tell you whether your installation of XP has been activated.
If that entry isn't there, go to Start>Run and type in (or copy and paste from here) "oobe/msoobe /a" (without the quotes), click OK.