Being a systems engineer, I'm glad I can fix stuff like this myself, but the best advice I can give you, which I practice myself, is to have more than one computer if you depend on it to make a living. I have three, so if any one of them fails I can always wait till I have the time to deal with it, in the mean time I'm not down.
To get to your system.ini, you can go to Start, Run, type in "sysedit" (without the quotes), this is a left over from 95. Or you can go to Start, Run, type in "msconfig" (without the quotes), the second tab from the left is the system.ini, you can edit it there if you must.
At this point, you should just back up your documents, export your bookmarks, cookies, email messages, address books, etc., and make a boot disk by going into Control Panel, Add and Remove Programs, reformat your C drive and install Win98 fresh. Reintalling an OS on top of a corrupt one doesn't work well, chances are you'll spend the time just to get the same crashing problem.
I deal with firewalls all the time, these personal firewalls work well, but they're always running in the background and sucking up CPU cycles and RAM.
The most basic kind of firewall is a packet filter, it has to compare each incoming packet with the rules so it will introduce some propagation latency, as does any switch and router. If you have broadband, you can get a Linksys router that runs network address translation, it will free up your computer from having to inspect each incoming packet.