Can i update to service pack 3 even if i don't have service pack 2?

May be...

Yes you can and here is how to do it:

Left-click on Start | Left-click on Programs | Left-click on Microsoft Update | Left-click on custom | Left-click on High Priority | Left-click on Review & Install updates | Restart

Hope that answered your questions,

Greg

Yes of course. Windows XP Service Pack 3 includes Service Pack 1 and 2. You can download using Windows Updates on your computer. Click on Start, Programs and then Windows Update on your computer and that should start the update.

and where can i download it?better if free.