One thing that is great about Ubuntu is the software repos. They make installation of applications easy, and keep them running pretty well up to date.
Sometimes the software in the repos isn't what you want or need. For example, Ubuntu 10.4 doesn't have the most recent version of WINE. It may be the most recent version that you should expect to run reliably, but it won't run the current version of Steam, for example.
So how do you get a more recent version?
add this to your software sources (system, administration, software sources. Select the other software tab)
Close the Software Sources window, and this will force a reload of the sources. You can then install WINE via synaptic, and you should be good to go for Steam installation.
Either Set WINE to function as Windows 7 as the default, or specify that Steam will run as Windows 7, and you should be all set.