I've had no problems with either SP1 or SP2. You can order an SP2 CD at no cost direct from MS at their website... delivery has been very fast (less than 5 business days in my case).
The service packs are predominantly security/patch related... you should see no change in performance (though I imagine with your hardware, XP doesn't run very fast... 192mb ram is not a lot). If XP Home works for your situation, why would you consider spending money to upgrade to XP Pro? IMO, you would be better off taking that money and adding more ram to your laptop... then you'd see a performance increase.