No one can tell you that you, without a doubt, will not run into problems. But neither can they tell you the same about anything you install. I've personally done over 60 SP3 installations on a variety of desktops and laptops and have yet to have any service pack induced problems with any of them. About the only thing I would recommend is not doing this via automatic updates but by downloading the complete file if you can. It's over 320 megabytes, however. I'd do the updates after a good Windows cleanup and fresh shutdown/startup. Disconnect the PC from the internet and disable any AV software during the process. This update takes some time so, with a laptop, don't run it on the battery. You might consider turning off the screen saver as well. All should be ok.
I have an older HP desktop comp. model 750n. Will installing SP3 cause me problems? I also have a sony vaio. Both are windows xp ops.I have downloaded all the updates except SP3.