I used to use a computer with Win 98 on it (now I have XP and have a firewall, and an admistrator account locking my hard drive and also have AOL's anti-virus and anti-spyware), but when I used 98, I used SPYBOT-Search and DESTROY (very good and free). It is used all over the world and WILL ACCEPT donations, but it is not a business and never asks for them except on it's website (it simply ALLOWS donations), but there is no TRIAL period to use the software. It is a labor of love in tribute to a girl he loves.
I always found the program to be very useful, it digs deep into the computer and finds things that you would never know were there and explains and identifies the files very well, has good online documentation and put other anti-virus programs that I've used to shame (it also has regular free updates and you retain complete control). Now it can also be used with XP.
http://www.safer-networking.org/en/index.html
Don't click anywhere near the box on the right (that's a third party software offering)
Read the recommendation here...
http://www.pcworld.com/downloads/file/fid,22262-page,1/description.html
This can be a reference for the files that are found.
http://www.spywareguide.com/index.php
http://answersthatwork.com
can also provide a reference of rogue files. Click on "TASK LIST" and next page click on the first letter of the file you're searching.
Pressing CTRL, ALT, and DEL (TASK LIST) 1 time but all 3 at the same time can show what is presently running on your computer.
CTRL H alows you to delete your history.
Pressing the "Windows key" F will allow you to search for files and get details about them.
To find the "Windows key", click START, click on RUN, and enter "osk" and press enter. The "Win key" is the brightly colored one (this is meant for the handicapped, that's why you never saw it before).
(remember to install it INSIDE your administrator account, not while your on the internet). If you don't have an admin. account, you should make one in Control Panel.