Firewall issues with Apache? Nah.
Apache is definitely your best choice for several reasons:
- small memory footprint
- low processor utilisation, whether the site is loaded or not
- cost
- stability
- security
- compatibility
You might be best grabbing a WAMP distribution (Windows/Apache/MySQL/PHP) that would be comparatively easy to install. Installing Apache can be tricky at times, but is always worth the effort.
The only firewall issue I can think of is that you might need to set up port forwarding on your router if you want to allow external access to the web site.
I wouldn't recommend going back to IIS 5 - not when Apache is so much better. IIS 6 is pretty good, but you may not have access to it.
You can run ASP code on Apache servers, but I would recommend making the (relatively easy) transition to PHP. Code processing is much MUCH quicker, and because PHP is so widespread, there are plenty of script libraries out there. Plus one of your best friends happens to have a fair amount of PHP experience.
![Wink ;)](https://www.computerhope.com/forum/Smileys/classic/wink.gif)
Oh - that's another reason to install Apache too!
![Grin ;D](https://www.computerhope.com/forum/Smileys/classic/grin.gif)
PS Where in the blazes are you going to find time for this freelance work?!