Despite deleting them, MSBlast/Laugh continue to appear

Update Windows using Windows Update, and keep a good virus scanner running in memory all the time.

If you can identify where the viruses keep getting to your computer from you can take safeguards to prevent it. I suspect, though, that the viruses were never correctly removed in the first place. What virus scanner are you running, by the way? And has it been updated recently?

Try running McAffee Stinger, it should remove the viruses you mentioned.

You might want to also run Spybot.

Some viruses write themselves onto areas of the hard-drive in ways that circumvent anti-virus software.

If you've tried removing it with a good anti-virus, but it still shows up, your only alternative is to do a complete hard-drive re-write, and even then, it's only about a fifty-fifty chance that that procedure will remove a tenacious virus. You may be left with the only other alternative: replacing your hard-drive.

Good luck.

The viruses put keys in the registry that simple deletions do not remove.

It is completely false that a re-formatting of a hard-drive is necessary (though it's sometimes easier than to deal with the virus) and it's completely false that replacing your hard-drive is EVER necessary for virus removal.