Boot time is affected by cpu speed,memory and hard disk. if your low on memory, say 128 or less, the computer will need more virtual memory/page file which is slow. If your running 512 meg or more the computer can load everything into memory and not use the page file. If the cpu is slow it wont matter what your hard drive speed or memory is. A 7200 rpm drive will boot faster than a 5400 rpm drive although not much slower. Drives running on an ata 100/133 will boot faster than one on ata33/66.
Soooo, many things afect boot time especially the number of programs you have running at boot: virus scan, messenger programs, Kazaa and such. With windows XP/2000 you can cut down on boot time and memory usage by disabling or setting to manual many of the services that arent needed for you computer.
Check here for info:
<A HREF="http://www.blackviper.com/WinXP/service411.htm#Universal_Plug_and_Play_Device_Host" target="_new">http://www.blackviper.com/WinXP/service411.htm#Universal_Plug_and_Play_Device_Host</A>