I have a WRT54Gv8, and I want to hook it up to my computer thru ethernet, install Linux, install aireplay, and try it out. But will packet injection work? I can't find a solid answer on the topic that isn't 4 years old. Thanks.
WRT54G V8 Has only 8MB of RAM and 2MB of flash: http://www.dd-wrt.com/wiki/index.php/Linksys_WRT54G_v8.0_%26_v8.2
It is not really powerful (by means of memory) enough to do any reasonable packet injection.
It has no USB port so no easy way to overcome general lack of memory.
Thus it makes a good WPA2-PSK and NAT home gateway. (dnsmasq+dropbear+hostapd will take 5 or more MB)
On the cheap end of linux routers i would recommend ones from TP-LINK
Packet injection on Linux hasn't changed appreciably in the past 4 years. You'll be fine.