You can use Opus to read/write Linux Ext2 and Ext3 partitions simply by using one of the following programs:
http://uranus.it.swin.edu.au/~jn/linux/ext2ifs.htm (read-only)
http://www.fs-driver.org (read/write)
These tools allow all Windows programs to see the Linux partitions as normal drives. Reports are that Opus integrates well with both.