When TweetDeck was released in Beta a month or so ago, many Android users rejoiced as it’s one of the most popular iPhone Twitter clients. Xperia X10 owners couldn’t join in the celebrations though, as the Beta was released for Android 2.0 and above. At the time, the creators of TweetDeck said that while the beta will only support 2.0 and above, the final version should be able to support lower versions of Android.
TweetDeck is still in beta but, more builds have been released. From the site it still looks like the app is only available for 2.0 and above. Searching for the TweetDeck app via the Android Market on an X10 also appears to confirm this, as the application is no where to be found. I can however confirm that the Sony Ericsson Xperia X10 does indeed support TweetDeck.
You will need to download the app directly from the TweetDeck site, which you can do here. You can either download it straight from your phone and install straight away, or transfer it to your phone from the PC and use a file manager to browse to the location and install the APK. You will however need the ability to install apps from a third party enabled. Something which is, unfortunately disabled on AT&T branded Xperia X10 handsets.