I have windows 98 and Works 2000. I receive e-mail attachments from a mac and I am unable to open them. Can anyone help me?

Not easy to advise when you tell us absolutely nothing about the attachments. What kind of files were sent? What format? Does the filename have a suffix (i.e: ".tif", ".jpeg", ".rm", ".exe", etc)?
If you have ann app that is supposed to open that type of file then you save the attached file to your HD and use the app to open it. There's no 'magic bullet' used to open ANY file. You should know what you are trying to open, and choose an appropriate app to do the job. "Double clicking" on something doesn't mean it's just going to open like magic. Hunters know what they are looking to shoot and use the appropriate gun. Same goes for you.

Pica (Virex makers) have a windows program called MacDrive 98, which opens mac files from cross-platform applications, like office and claris and adobe etc. If you expect a lot of mac files it may be worth investing in this, otherwise just email your friend and ask for simple text or pict or gif or jpeg attachments etc. It is probably easier for the mac sender to make the attachment more PC friendly.

To get the mac sender to ad the extensions to the
files is good. To ad them yourself might work. If
you know the file to be an image try adding the
windows extension of .jpg to the file (JPEG =
common image filecompression format for sending
images) if text try .txt etc. This often solves the
problem. If you are going to recieve a lot of files
from macs, get Aladdin expander (free and a great
tool anyway) and tell the mac users to compess
the files with stuffit or dropstuff prior to sending
them. Then Expander will ad proper PC file
extensions to the file upon recompression.