There are many reasons why windows is very slow during start up. One reason could be your computer has viruses or to much graphics that it slows down. Before any virus infects the computer you should install an anti virus on your computer and so far the best computer anti virus that I used is ESET NOD32. Here is also one trick for you so that your computer will have a faster start up.  Click start and click run.  On the command type MSCONFIG and click on the start-up tab as shown below.

On the image you can set whatever programs you want to start when you turn on your computers.  On my Laptop whats running after turning on is the SynTPStart this is for my touch Pad Driver, I also have Rainlendar runnig on my computer and this is the best calendar for XP so far I have used.  cftmon is a windows application that is on startup, GoogleToolbarNotifier this is a notifier that whenever the default toolbar is not google it gives me a prompt if whether I still want google to be my main toolbar.  and the lasting is I have btdna running on my system this is a bittorent application used when I download movies, music and other big files downloaded in one time.

And also virus are also ran after logging in so that is why most virus disables the MSCONFIG command on the computer.  If not disabled and you can see applications ran on startup you can always uncheck the button and if you think the applications ran are not important you can uncheck them all.  If you want a twaek to improve the booting of your computer, Go to Start Menu and Click Run, Type in “Regedit” then click ok.  Find “HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Dfrg\BootOpt imizeFunction” and on the right Select “Enable”.  right click on the item and select modify, Change the value to “Y”.  Then restart your computer and this should do the trick.