By boot - do you mean for Windows to load (at least for the desktop to appear) or for things to settle down enough for the desktop items to become useful?
If you get a few timings down for a base measurement, you will have something to compare as you start trying to make adjustments, instead of just saying "well, I think it might be faster" (or it is worse). By taking a few notes at first, you will be able to say for sure it is faster, or it is not faster instead of guessing after you make some adjustments.
I quit using McAfee (free
from my ISP) a long time ago because if it was running, it was terribly slow and took a long, long time. McAfee updates were just as painful. It also does not have what I consider basic feature flexibility even in the full fledged version, it never found a darn thing, etc. I will never recommend it.
I switched to MBAM, SAS, and AVG since they seemed to be helpful in finding the most problems (not on my computer of course). They are free, reasonably speedy and find something more than just inedible tracking cookies for their effort. They must be run manually though - for the free version, which is fine with me. One AV program is never enough for your arsenal since no one program can know about everything, so stick with the ones that have earned the most respect.
I also don't rely on Spybot or Adaware - unless you are hungry for cookies. I have also fixed a lot of problems that start with "I installed Norton and now..." , so I am not sure about that either. They have all lost their luster with me. ut everyone has their own opinions.
Once your system is settled down after a reboot, go to Start, Run, msconfig <enter>. Look at the Startup tab to see what XP loads on startup (boot). Do you see anything you don't know for sure what it is? Uncheck it so it will not load next time and reboot. Measure your new time now. You can always turn it back on later if it causes any problems. This does not remove the program - just keeps it from running at startup. If you don't know what it is, use Google or ask here to figure out if you really need it or not. I have more unchecked than I do checked.
Then look at the Services tab, check Hide All Microsoft Services. That tells you some of the things that are running right now. Do you know what everything is and do you need it? Turning things off does not uninstall them - it just disables the service so it won't start on the next reboot, same rules as above. Pay attention to the ones that are checked AND running. If it is checked and not running you can leave it or uncheck it to keep things tidy.
Folks will sometimes just decide to just start uninstalling applications (from Add/Remove programs hopefully) and generally not not see any difference and sometimes introduce worse problems. It is not the number of things you have installed, it is whether they are running or not. Some things will add a service or put something in the startup as a convenience for you even though you only use the application occasionally . You can leave the program installed, but just turn off their rude convenience features. Adobe updater is a killer.
Autoruns and Startup CPL will give you all the information MSCONFIG does plus a whole lot more, but I would try the easy stuff first. Nothing to download - you already have it. Save those tools for later. Task Manger will help you understand more, but try the easy stuff first.
Here is a good tweak that will shave about .5 seconds off your XP kernel load time. Adjusting the boot order in your BIOS to boot from the hard drive first and then the CD instead of the other way around. There - a whole .5 seconds! Is your XP configured to give you a whole 10 or 30 seconds while you stare at the screen deciding how to boot? Change it to 5 or zero - just boot and do it now.
These are basic things that will let you understand more about what is happening behind your back. Then you can decide what action to take.
I postulated a while ago that no matter what you do, your computer will never run like it used to when it was new, and that no matter what you do, it will never be fast enough
. Accept that fact with you new understandings and you will start to feel a little better as you work on this knowing you are doing the best you can.