Yes, you can create an Ext2 partition on your SD card, but you'll also need a ROM that supports A2SD (apps to SD, not to be confused with Android's built-in move app to SD card function) in order to save space on your internal memory. To get an Ext2 partition, the easiest way is to format your SD card from within your recovery (both CWM and malez give you option of creating an Ext2 partition), but don't forget to backup everything on your SD card first.
Next, you'll need to enable A2SD from within Android; the method varies from ROM to ROM, so you'll need to read up on how to do it with your ROM. Once that's done, you can move your /data partition (all user installed apps and all apps' data), your dalvik cache, and/or your /cache partition to the Ext2 partition on your SD card, just make sure your Ext2 partition in big enough (the total size of all internal memory on a Liquid device is about 512MB AFAIK, so set the size of your Ext2 partition accordingly).
There are also other methods of freeing up space. For example, you can move certain apps to your SD card using Android's built-in function (though remember, only the apps' resources will be moved, so while a 30MB game might be 1.5MB after moving it to your SD card, a 16MB maps app could be about 5MB, as the code of app needs to stay on the internal memory of the device) or, if you have a ROM that lets you do this or if you use TitaniumBackup, you can move any app (even ones that don't allow it normally) to your SD card this way.
You can also try cleaning the caches of your apps: you can do this manually, or download an app (like CacheCleaner NG) that does it all in one go.
And then, of course, is the easiest way to free up storage space: delete any unused apps and/or the data of apps that you don't use often and that use a lot of space for data storage (for example, I know the Orbot, the Tor client for Android, uses about 6MB for its data, even though the app itself is around 1MB in size).
EDIT: Oh, and if you're really up for it, you can repartition your internal memory, but seeing as you asked about how to create an Ext2 partition on your SD card, I don't recommend you mess around with your internal partition layout.
Edited by Delnar_Ersike, 14 June 2012 - 12:14 PM.