Click on Start - Run
Now type: msconfig
This launches the utility.
Click on the Start Up tab.
If you are unsure about any thing in there paste it into Google to find out if it is essential.
The computer will still boot if you Disable All but you may lose some functionality of things like your mouse.
After making the changes reboot your machine.
The changes are reversable but if all is okay you need to tick the box which says 'Do not show this message again' after you have rebooted.
For some reason in XP doing that stops it from reverting on the following boot.
Apart from the mouse and keyboard (If you are using wireless) all programmes which are starting at this stage will start anyway as soon as you request them.