For FPS games your ping will be far too high.
However the bigger issue is the traffic shaping they perform when you try to play. Having played with a mobile broadband connection (Three - a UK company) for 4 weeks, I've discovered that regardless of how little bandwidth your game uses - say 3k/second, the network will cut you off if you exceed even 2k/second after about 1 minute.
Presumbly they have some form of neural network or learning software in place that blocks your UDP packets after a set period. It may not be the same on HughesNet but I'd be wary.
It's crazy that you can download files, browse 500k per page websites like Flickr but they won't let you stream far less bandwidth for games.
The solution I use is to host an adhoc wifi network on Windows 7. Then once the game is blocked, I kill all the connections to that game using Netlimiter. The number of disconnects I get generally drops after peek hours, but they're very aggressive with the "learning" and blocking of the gaming traffic during peak hours.
It's ugly and extremely cumbersome but does work slightly better than a reconnect via the modem.
You might also want to get an antenna for the 3G USB modem, either a clip one or an outdoor one.
Here's a link on Networking with the Xbox 360, from xbox.com.
Here are a couple of links from instructables.com that seem to cover exactly what you're trying to do.
And here's a video of the same thing.
Best Answer
It's really difficult to say as it depends on so many other different factors as well. At first glance your download speed look acceptable, but upload speed is pretty low and your ping is fairly high as well which will both have an impact. There's also the issue of contention, which may see your broadband speeds rise\fall depending on how many other households are using the line at that particular time.
Then there's the type of game\service you want to use. Some games require more bandwidth than others, for example a first person shooter game will require a lot more than say, a turn based game like Uno. Streaming films also requires a lot, depending on the quality.
So taking into account these factors here's my recommendation:
Heavy bandwidth games (COD, Halo): Most likely have lag, and be hard to play online
Medium bandwidth games (Mortal Kombat, SFIV): Should be fine, may have some lag
Low bandwidth games (Uno, Texas Hold 'Em): Should be fine
Movies: May struggle with buffering and stutter
although don't take this as definitive, you can hook up to xbox live for free and you usually get a months free gold membership too so you can test out some online gaming before you commit to a paid membership, and I'd advise you ultimately to do this.