A dual drive system offers less opportunity for clever schemes but the following should provide a simple starting point.
Partition sda sdb
---- ----
1 boot lib
2 swap news
3 /tmp swap
4 /usr /var/tmp
5 /var /home
6 / (root)
If you use a dual OS system you have to keep in mind that many other systems must boot from the first partition on the first drive. A simple DOS / Linux system could look like this:
Partition sda sdb
---- ----
1 DOS lib
2 boot news
3 swap swap
4 /tmp /var/tmp
5 /usr /home
6 /var DOSTEMP
7 / (root)
Also remember that DOS and Windows prefer there to be just a single primary partition which has to be the first one where it boots from. As Linux can happily exist in logical partitions this is not a big problem.