Windows XP Internet Connection Sharing: Port Forwarding Difficulties

I have properly configured ICS with two NICs on one of my Windows XP machines (chii.usr.local), and the interfaces look like so:

Ethernet adapter 3Com:

Connection-specific DNS Suffix  . :
IP Address. . . . . . . . . . . . : 24.129.135.46
Subnet Mask . . . . . . . . . . . : 255.255.255.252
Default Gateway . . . . . . . . . : 24.129.135.45

Ethernet adapter Marvell:

Connection-specific DNS Suffix  . :
IP Address. . . . . . . . . . . . : 10.0.0.20
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : 10.0.0.20

Three other computers on the network exist:

rurouni.usr.local -> 10.0.0.10 (Debian GNU/Linux)
takkun.usr.local -> 10.0.0.11 (FreeBSD) 
vesper.usr.local -> 10.0.0.30 (Windows 2000 Professional)

All three machines are configured to use 10.0.0.20 as a gateway to the internet; consequently, all three machines are properly functioning with full internet access.

The problem is that both takkun and rurouni are running various services that need to be accessible by common internet users. To attempt to solve this, I began opening ports and forwarding them to the appropriate internal addresses. In the end, both my DNS server and IRC server worked flawlessly, as both were viewable worldwide; the HTTP server and a few other services did not, however, work out very well.

If you are reading this right now, and my problem has not been solved, you can run a few queries to the domains jamiansnow.com or neverendnight.com to see what I mean. Indeed, the DNS queries will run perfectly fine, but the HTTP requests are as good as gone. For some reason, Windows XP's "Services" control is allowing _some_ connections through on the ports and internal addresses that I have specified, but it is seemingly _ignoring_ other entries.

Here is how I have set things up:

3Com Interface Properties → Advanced tab → Internet Connection Sharing: Settings... → Services tab → [x] DNS → Edit... → IP: 10.0.0.11; External Port: 53; Internal Port: 53

This part works like a dream.

3Com Interface Properties → Advanced tab → Internet Connection Sharing: Settings... → Services tab → [x] Web Server (HTTP) → Edit... → IP: 10.0.0.10; External Port: 80; Internal Port: 80

Obviously, this part does not work at all.

Also, before anyone comments on whether or not it is the actual service that is or is not working: yes, the HTTP server works perfectly fine internally, and yes, the HTTP server worked perfectly fine when I was using a router earlier today (the router needs to be replaced, this needs to work in the meantime).

I would _highly_ appreciate any background information that will lead me to solving this problem. I have no faint clue as to why some of the port forwarding entries would work, while others would not. Time is quite crucial, so as many replies as possible are welcome. Thank you very much, in advance.