I'd say in the short term, yes, but in the long term you'll not be wasting any time because the extra performance will more than make up for it after even as little as a fortnightGentoo + XFCE if you want lightweight and superfast (although you pay for that speed in compile time).
^^ but I would add that if you are wanting to learn more about computers, irrespective of OS, this is a fantastic way to learn. The Deep End.Word of warning though: Gentoo is NOT for a beginner, there is no installer and it takes forever to install anything. Truly understanding all the use flags for compiling applications properly takes a while too, until then you will be building bloated apps for bloated kernels.
Have you tried the latest version of Ubuntu? 7.10 is very, very quick, even with the 3D desktop [Compiz] enabled. Though of course I wouldn't recommend 3D desktop on a low-end machine.