However - there is a project on SourceForge that allows you to access Ext2 partitions from Windows. Now - you may be thinking 'But I use Ext3!!' - well never fear. Ext3 is backward compatible with Ext2, which means that these partitions will work (you just won't get the journaling features of Ext3 while accessing the disk from Windows).
After installing this program you can mount a virtual hard disk, and then use the Ext2 volume manager tool to assign drive letters to the virtual hard disk.
This all works perfectly on Windows XP / Windows Server 2003 - but I found it a bit problematic on Windows Vista.
If you are running 64-bit Windows Vista (like me) you will need to enable 'test signing' in order for this tool to work. You can do this by opening an administrative command prompt and running:
Bcdedit.exe -set TESTSIGNING ON
Also, on Vista you need to launch the Ext2 volume manager tool 'as administrator' in order for it to work properly. Finally - once a drive letter has been assigned - it will only be accessible from administrative command prompts (not from explorer). While this makes it a bit painful - it is still quite useful.