Ever heard of ext2ifs? It's an installable file system driver for Windows, and it will let you connect an external USB drive with the ext2 file system to a Windows system and read it.
This is not an ideal solution for many folks. Any portability of that disk will be lost outside your environment without asking other folks to install the same driver. Also, although it will read EXT3 filesystems, I don't believe it supports the journaling, and I'm not sure it will even allow you to write to them. Reading the FAQ
http://www.fs-driver.org/faq.html turns up several other issues with EXT3.
I look at this as another tool in the toolbox, but not a method of supporting a disk on a day to day basis.