Your lspci output shows only one Ethernet controller (the wired one, a MCP79 which should be supported by the forcedeth driver). Doing a web search, I found a curious piece of information in a review of your motherboard: "The WiFi module [...] connects to the board via a USB header". If that is true, the information you want will be found not in lspci, but in lsusb.
After finding the correct line in the lsusb output, you can do a search for the ID (which will be something like 1d6b:0002) to find other people discussing the same hardware (people usually post the USB ID in that format when asking for help).
It seems Linux Mint is based on Ubuntu 9.04, which uses a 2.6.28 kernel. You could try a more recent kernel (Ubuntu 9.10, which should be released late this month, uses 2.6.31) to see if there is a driver for your device.
EDIT: Now that you posted the lsusb output, I can see that 160a:3184 is your wireless card. A quick search shows it is a VIA wireless card, apparently called VT6656. It seems there is a driver from VIA for it, and it seems to have been added to the staging tree for cleanup and possible future inclusion in the Linux kernel. See also Ubuntu bug #162671.
Basically the main issue with thumbsize adapters is the worse signal to noise ratio (SNR) for both signal received and transmited. Wi-Fi is a radio, so you can get the idea: the better the signal the better the sound you hear. Put a metal foil around your logitech transmitter and it will block the signal almost completely. Put it on extension cord so there will be a direct visibility between adapter and keyboard and it would work perfectly.
WiFi module itself can be very compact, there is no benefits in having a large board (except that you can install additinal shielding of wifi module, so it's better protected from outside noise), but antenna quality and placement can make a huge difference.
In 802.11n multiple antennae are required to achive speed higher than 150 Mbps (150 Mbps per antenna) so that's why the 150 Mbps limit.
The quality of the Wi-Fi chip itself, of course, also matters. All statements above suppose same quality chip on both adapters.
All this can become more complicated in case of using USB 3.0 devices on USB 3.0 ports. In that case a closely placed Wi-Fi (and Bluetooth) USB-adapter can experience significatn SNR drop.
@Breakthrough also mentions two other possible limitations of the USB connected device, but personally I'm not sure that whey are major issues, I try to explayn why:
I can't actually find any power consumption for Wi-Fi chips, but I found this, it says that 210 mW is required for 40 Mbps transfer. Also this study (and many others with similar results) shows that typical Wi-Fi router emission level is about 100 mW, and 500 mW for outdor high-power points. I can't be 100% sure (since I don't know chip-to-signal power ratio, I would assume 10%), but with a 2500 mW of USB available power I think power limit is not a concern.
As for the USB 2.0 speed, it's supposed to have transfer cap of 280Mbps, so it'a also can't be a major limit, at least from a specifications point. However 450 and higher speed 802.11n connections would be limited indeed.
Best Answer
I found where they sell them in a 2 pack on amazon here. There's one review that goes into some detail about how it didn't work with Fedora or OSX, as well as the chipset which if you do decide to go for it should allow you to find the drivers. However, at a glance, not being able to find a web page for whoever makes these, and the negative review i'd have to give it a pass. The company selling them does respond to the review, but it looks like you'll have to build your own kernel if you even want a chance at this working.
The chipset they state is an RT3070.