There will likely be an SP3 at some point, maybe even an SP4 before XP is put out to pasture, but that's about it. When SP3 will show up is anyone's guess. After Vista SP1 is about all anyone really knows for sure.

If you went out and bought a retail disc that had SP2 slipstreamed in, it would be exactly the same thing as an older installation disc that you then installed SP2 onto. It's not like when Microsoft released Win95B which was OEM only, but even then, the only change was the addition of FAT32.

Just install what you've got, and make sure one of the first things you do is to apply all the necessary security updates after that.