DLL file problems

My friend is running Windows ME and has suddenly been having a lot of problems with DLL files. When running Internet Explorer (it was version 5.5, but I upgraded it to 6.0) and Outlook Express, various error messages come up complaining about DLL files.
I was wondering how we’d replace the DLL files. I know how to extract one file at a time using the extract command, but that would take forever considering how many different ones she’s had come up as errors.
Also, is there any way to tell if DLL files are corrupt? I tried running Windows help to work out how to extract multiple files, and that wouldn’t run due to a DLL file error.

From the Microsoft web site.

Thanks, I’ll get her to try that.

Doesn’t WinME have System Restore checkpoints? Hopefully, there’s one right before the IE6/OE upgrade. If so, roll back to that point and stay happy with IE5.5

System File Checker Is Not Included in Windows Millennium Edition