Just to get the terminology straight.
You are running a XP on a Mac that is also running Tiger and thus you have the older version of the bootcamp drivers on it. (bootcamp has nothing to do with running windows, it's just a collection of drivers for hardware).
SP3 should install fine unless there is a problem with one of the drivers that apple supplied. However you can always find replacement drivers from manufacturers websites or download the leopard bootcamp driver set.
Note that because neither bootcamp nor your version of OSX has anything to with your ability to run windows, the leopard bootcamp driver set doesn't actually need leopard to install.