If I understand correctly you want a way to use your PC proxy connection when you're away from internet sources?
In order to use your PC proxy you'll still need internet access at your location (and an open port or VPN access to your PC). If you were using a laptop you could use Wifi, wired, cell phone tethering, or a cellular access card (the latter two will incur fees from your cellular provider).
The iPod Touch does not have any options for accessing the internet other than through Wifi although there may be hacks to use wired via the dock and some adapter cables, and cell phone tethering would not be impossible as long as you had the right hacks and cables, assuming that they exist. To my knowledge there is no cellular connection card that utilizes the dock connector at this point in time although such a device coupled with a mic attachment and some VOIP software could provide almost iPhone like functionality albeit through a more awkward device but would only require a cellular data plan.