Here is my two cents...

I am running NT...A compaq 3000 series dual porcessor machine. It only has Orcale on it and I do not use it ro run enterprise manager or any of the the other oracle tools. It is strictly a server box. I have Oracle configured to use 1.5 gig of the 2 gigs of memory that is on board. I have had great sucess with this, as my database size is less than one gig and the whole thing sits in the buffer:0

IMHO, the 50% rule of thumb is fine until the amount of memory goes past an upper limit. 512 MB of memory of the database and NT to share for their processes seems more than enough to support them well.

John