Buy a new one... 2.2GHz AMD with 896MB RAM is old skool IIRC...
Mine's an AMD 1700+XP running at 1.57Ghz, 1Gb 133Mhz SDRam and takes 37 seconds to boot Windows XP Professional with SP3 and LAN running.
If you've got a desktop full of icons. usually it workloads a profile loading too, clean them up (put them all in My Documents) and use shortcut icons. Sometimes the blues front end slows it down too. you could try turning it off.
More program installs usually slow down performance too, go through your add/remove folder too and uninstall programs you rarely or never use. Might even be the wrong memory too, you could have 2 memory sticks and one of them is running slower, so it slows down the rest too.
*** Edit, someone else has suggested that above, **