XP Service Pack 2 upgrade to SP3 question

Hi, I have a Dell Dimension 5150 which is now about 6 years old. It came with Service Pack 2 and in order to acquire a few new pieces of technology like a smartphone I have been told that I need to upgrade to Service Pack 3 for it to work properly. I remember all of the fuss about people having problems with SP1 upgrading to SP2 so on a hunch I thought I would see if there was the same kind of thing with SP2 to SP3 and I have noticed by searching this forum there are a lot of people who do seem to have problems upgrading. I was wondering if someone could please tell me if my computer will upgrade to SP3 without any issues. Or what might cause issues while trying to upgrade. I have a couple of external hard drives so I can move the majority of the contents off my computer if that is likely to cause a problem. In fact, now I think about it, I use one of the external hard drives to store all of the big things like my iTunes folder anyway so there isn't really that much taxing the computer. The only thing I have upgraded on my computer over the years is the RAM from 1GB to 3GB. I haven't actually noticed a difference in performance with it. And before anyone asks, the RAM was bought from Dell, I even spoke to them directly to find out which one would work best. So it's not like I bought one from a dodgy site. I would really appreciate any help you can provide, as I am/was kind of hoping not to replace this computer until the end of next year as it still works, for now at least. Thanks, Chris.