I have an old laptop that has a 30 GB HDD (IDE 2.5") and I thought of giving it a little boost by replacing the HDD for a SSD.
Would there be any compatibility problems if do that ?
Does Windows XP support SSDs ?
Windows XP supports SSDs, no problem here.
Although the SSD market for 2.5" drives using the PATA interface has been largely ignored, some manufacturers (e.g. Transcend, KingSpec) do offer those. Also make sure to get an SLC type SSD for better performance (as opposed to MLC)).
How old are we talking? I just put an SSD in a Core 2 Duo Lenovo machine that's probably about 5 years old, it was like getting a new computer.
Modern computers seem to be bottle-necked more by HD speed than CPU. If we're talking a Pentium 3 though I'm not sure you'd see an appreciable difference.