Experience of reading ext2/3 volumes from windows varies considerably. This is a summary of what happened with them on XP home on an eeepc.
ext2ifs "Ext2 Installable File System for Windows" allowed me to re-label the internal hdd volumes, but not the usb ones, but it did not allow me to actually read the volumes. http://www.fs-driver.org
ext2read works well as a read only service but not for usb hdd's. http://ext2read.sf.net
ext2fsd appears to work well with all internal hdd's and usb hdd enclosures. If set to "automatic" the volume manager will re-label drives on plug-in and they become available in explorer for reading and writing. http://www.ext2fsd.com
Using ext2fsd made the linux partitions all available r/w in cygwin. http://www.cygwin.com/
Virtual Volumes is a beta multiple volume type reader with support developing for raid, vm's, etc. Given the strong warning of it's beta status, I did not test it. http://www.chrysocome.net/virtualvolumes
NOTE :- If the ext3 filesystem is not shut down cleanly in windows the subsequent boot process by linux will probably force a fsck because journalling was not completed. Similarly, if an ext3 filesystem is crashed in linux and subsequently examined by the extfs reader in Windows, it will likely fail because journalling was not completed.