You can disable UAC, that may make it load faster. You can also disable some programs starting automatically using config.sys but at the end of the day I think you'll just have to suffer Vista's long load time.
Also using Ccleaner may help (free software that cleans out unwanted detritus from your hard drive)
Advice: Switch on computer; put kettle on, make tea/coffee. enjoy tasty hot beverage, return to computer - it will be ready to use
Odd, when you think how Win 3.1 boots to start screen in about 15 seconds - that's progress for you
Can you fire up MSConfig.exe and take a look at the startup tab - it could be that you have lots of things loading automatically. You can then uninstall those applications or configure them not to start when your PC boots. I have to admit, I personally wouldn't disable UAC - as although it can be a pain it does do some helpful things sometimes .
As flops as already mentioned, Windows 7 is quite a bit faster (especially on boot) than Vista - but I guess that would cost about £60 to upgrade (and I'd strongly suggest a clean install). My old laptop with a 1.3Ghz CPU works really well with Windows 7, but it chugged under Vista.