Upgrading to 802.11n on older Mac Mini

Apple's enabler wouldn't work, as the 2007 Mini doesn't have the right hardware.

USB dongles would work, OTOH: such as the one in your link.

BTW, there are also much smaller ones; for example, I have this one:

http://www.digicom.it/digisit/prodotti.nsf/ITProdottiIDX/UsbWave150Nano

... which might be available under other brands in your country; there are also 300 Mbps dongles (which however can be bigger in size, similar to a USB flash drive).

USB dongles (which are seen by the OS as another ethernet port) usually come with proprietary connection software from the manufacturer of the device's hardware (Realtek in the case of the Digicom dongle above): so it's not entirely seamless (but the connection can start automatically).

... But I'm not an expert on this, so others here on the forum probably know much more.

2) How much improvement will I see going from a/b/g to n?

What you do will determine if you'll see any improvement. For example, if you're only surfing the net, checking email, you may not see any improvement as your speed limit is with your ISP and not Wi-Fi. Many people have "basic" broadband which is less than 10Mbps. This is around 802.11b speeds. So upgrading to g or n will not get you any improvement.

If you're trying to share files between multiple computers within your own LAN, then you may see an improvement going to n. But it may only be noticeable with moving very large files. (i.e.: movies instead of Word documents.) Potentially it could help if you're viewing movies in the iTunes library on another computer (since it's all on the LAN and not through your ISP.) Listening to music from another computer uses less bandwidth so you likely won't see any difference between g & n.

4) How about this USB adapter?
5) How about getting a Airport Express and connecting to its Ethernet port?

Either could get you 802.11n, if you need to speed up your LAN. The USB adapter is straight forward, but it does require you to add a driver. Newer Tech's website shows the driver for 10.3, 10.4 & 10.5, but doesn't specifically mention 10.6.

Airport-to-the-ethernet port would work and wouldn't need drivers, but does require some skill configure...at least require a willingness to try. It's not that hard, but many people are put off by networking.

Me personally, I'd prefer not to have to install drivers since a future OSX update could affect the driver. So I'd be going with the Airport-to-ethernet option. (Actually, I'd be going with wired since you'd get 100Mbps or 1000Mbps (depending on the equipment), which is as fast as the real-world speeds you get with 802.11n (or faster) and has much less configuring than Wi-Fi and less susceptible to radio interference, and I do move very large files to the server on my LAN...but that's just me. 🙂 )

I'm moving to an older house and where the mac mini will be is not close enough to the ethernet outlet.

Be aware that to get the speed improvement of n over g, n uses more frequency space, which means that things that may not have interfered before on g, might have an affect on n. (n could take over 80% of the available space in the 2.4GHz space.)

The 5GHz band is less susceptible to interference from cordless phones and microwave ovens, etc., but doesn't penetrate walls as well as the 2.4GHz frequencies. So your range when using the 5GHz band is usually less when indoors and could actually be slower than g. This is the case for me. My Airport Extreme in the 5GHz band is very good when I'm in the same room, but barely travels to the living room, which is about 50' away through half a dozen uninsulated wood walls. An old Motorola 802.11g access point using 2.4GHz at approximately the same distance and amount of walls but in a different room gives the a stronger signal and faster speeds at that distance. Changing the Airport Extreme to 2.4GHz gives me the signal and some speed, but not as fast as when I'm in the room on 5GHz.

So you may want to see if performance will be acceptable at the other location before spending any money. You may find that n could give you worse performance.