[HOWTO] Wi-Fi Tethering on MIUI
Start the rom's wifi tether from Settings > System > Tethering & Portable Hotspot > Portable Wi-Fi hotspot.
You should be able to connect to it, but you won't be able to use the Internet.
Now set up the NAT manually, for which which I've found a tutorial online*. We'll want to connect ppp0
Open a root shell and enter the following. (Note that /proc/sys/net/ipv4/ip_forward is set to 1 automatically when we enable the rom's tethering)
iptables -t nat -A POSTROUTING -o ppp0 -j MASQUERADE
iptables -A FORWARD -i ppp0 -o wl0.1 -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A FORWARD -i wl0.1 -o ppp0 -j ACCEPT
Now you'll be able to access the Internet from your computer.
Disclaimer: I haven't tried turning it off yet. I assume you just remove the three rules and then turn off the rom's tethering.
*new users can't post links, so just Google "linux nat"