ahgar, since sbc is your provider, the problem is almost for sure the sbc software. I used to do support for them, and there was a serious problem with the yahoo software working with both dell and compaq computers running XP.
One of the problem files the sbc software installed was the "broadband client foundation", but there were a few other files, I think 2 of them that I can't remember that also contibuted to the blue screen problem or not even being able to boot insto safe mode.
I'd suggest you wipe the hard drive and do a fresh install on it, and then set up your sbc connection without using their software at all. You don't need any of it. If you're a fan of the yahoo browser, you can try installing that seperately from the sbc portal, but I would avoid it. It really is just a different "skin" for IE anyway.
The only thing you would lose is that with the yahoo browser, your favorites and addresses are stored on the server side, with IE you have to back them up yourself and save them to a disk or something.
Setting the connection up manually is a breeze, and should take a lot less time then installing the yahoo software anyway. All the dsl modems they've shipped in the last couple of years have PPPOE built right into the modem. In other words, all you should have to do is connect the modem to the computer, plug it into a power outlet & the phone line, open IE, and type the address of the modem into the address box of IE and click go. (Something like 192.168.0.1) The address should be right on the modem. If it's not, you can click on file - run and type in command and click ok, which will give you a dos window.
nopw type "ipconfig /all" without the quotes and press enter - that will give you all the information on ip addresses your computer is using. The number that is labeled "default gateway" is the address of your modem.
Once you've typed the address of the modem in the address box of IE and clicked go, you should see a screen to enter your user name and password. Type them in and click Connect. That should be all you need to do, and you should be good to go without installing the sbc software.
If you are using a dialup modem, well .... then you need to configure a dialer for windows to use. XP is different than 98 in doing that.
Go to start and click on control panel, and in the column on the left click on Create a new cionnection. Then you will have a wizard pop up that is similiar enough to the '98 wizard that you should be able to set up your dialup connection pretty easily.
Once again, your problem is 99.9% likely to be the sbc software .... give a fresh install and set your connection up manually and see how it goes.
BTW, when I first started using XP, I probably disliked it more than you do right now ....but when you get used to it, you probably will not want to go back to using 98. Although I did make a shortcut for windows explorer (cause I am no fan of "my computer" and for IE (I can't stand MSN explorer").