Yep - upgrade to Win 7
Sorry
Vista does have an extrememly long load time.
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