Let's get it over with and move on
You haven't installed any of the critical updates that followed SP2?? So much for you being careful! So how many known vulnerabilities that are being actively exploited on the net does your XP box have then? A few dozen at least?
Calm down! Actually, I forgot to mention previously I have allowed the critical updates to install. As I stated I did install/reinstall MS everything religiously through SP3 at least 10-15 times over the past few months. As a side note previously I also installed IE7 with disasterous results of some application software compatibility issues. If you don't believe me do a Google search for "IE7" and read the grief users have experienced and are trying to get rid of it. I reverted to IE6. Back on subject...randomly at power on boot up only, not restarts, I would receive "sys32/missing or corrupt config sys" related messages. As previously stated this required a reinstall of XP as the repair option did not work and a bootable diskette cannot be created if using NTFS drives. I additionally had to reinstall all of my application software. I soon became tired of doing that. The cause is not a virus. MS is well aware of this problem since about 2003 in fact documenting its' existence on their website. A Google search also discloses this is a significant problem other XP users have had. MS really doesn't know what causes it and recommends a couple possible courses of corrective actions to take both of which don't work. I upgraded the BIOS and still had the problem. So, it's a risk tradeoff. I preferred to stop at SP2 and boot up successfully each time compared to receiving the MS boot up config sys missing or corrupt death related messages and having to reinstall XP and all of my application software again and again and again. Like I referenced, read SP3 and tell me specifically what is included. You cannot do it. I am not blaming the config.sys problems on SP3. Whatever is the cause(s) predates SP3 by a number of years. At my son's college commencement two weeks ago the gentleman sitting next to me installs small business system computers. Our conversation soon turned to computers and I found it interesting that he didn't install IE7 or SP3 either on his home computer system. I had never met this guy before. Just because something is the "latest greatest" doesn't necessarily mean it is the best.
I have virus checkers and at each session I run diagnostic software, i.e., remove adware, malicious software and spyware; registry maintenance, crap cleaner to get rid of temp and internet temp files, deleting cookies, Winpatrol to be alerted on anything that trys to install in my startup that I can immediately delete if I don't permit it, etc. I do not leave my computer powered on connected to the internet 24/7. I decided to stop at SP2 and so far so good. I am almost a month free of MS killer "missing or corrupt" config.sys related messages which is a record. If I get the killer message again then I reinstall XP and the application software again.
Just another quick comment about internet security. Three years ago my credit card information was stolen from EBAY. I have a credit card I use only for EBAY I had not used it in the previous two years. I sold two items. Three months later I received a letter from a co. in Nebraska and was asked to call them. They monitor ALL Master Card and VISA purchases and compares them to your(Yes, this includes ALL of you reading this) purchases profile. I was asked if I had purchased $1,600 in computer items for Joe's Computer Shop in Chicago; clothes from Sears in Ann Arbor, Michigan, and a couple of other purchases. I responded "no" and immediately realized my CC information had been stolen from EBAY and told the rep how I knew. I was not charged a penny but the greedy vendors who failed to check the CC information suffered the loss did to the amount of approximately $3,000. Did you see anything in the media about this? No you didn't. If my CC info was stolen then how many hundreds of thousands if not millions of others, that may have included YOU, using EBAY had their CC info stolen? I immediately canceled my CC and received another one. So instead of chastising me you had better spend that energy being concerned about the security of your CC info on EBAY or Amazon or wherever else.
Believe what you will and do what you want and I'll do the same.
Ok...time now for everybody to pile on with their nasty reply posts, holier than thou pontificating, warnings and condesending and condeming comments. Get them over with now and let's move on to the next whatever subject.