@radiosilence:
It has no CD Drive.
If your laptop will boot from a USB drive and you can access a USB CD drive you could probably install from the USB CD drive. Alternatively, put your laptop hard drive in another system which can boot from a CD drive and install there, then move the hard drive back to the laptop. There will probably be a couple of minor tweaks required after moving the drive.
@radiosilence:
It only has one Ethernet port.
If your gigabit switch supports VLANs and the laptop ethernet supports VLANs you could use the switch as a port multiplier to provide multiple "virtual" interfaces to pfSense.
@radiosilence:
Is it worth my time? It has 512MB RAM, an Intel Pentium M 1Ghz CPU. It'll be serving four or so users + some on wifi and I want to do things like QoS and traffic reporting/controlling like this: http://i.imgur.com/cXi0t.png (not sure what module that is though).
The CPU and memory are probably more than adequate.