Amount of RAM needed to support a growing lucene index?

["lucene user"]

Hi, Folks -

Two quick questions - need to size a server to run our new index.

If I have an index with 111k articles and 90 million words indexed, how much
RAM should I have to get really fast access speeds?

If I have an index with 290k articles and 234 million words indexed, how
much RAM should I have to get really fast access speeds?

Any other advice about sizing a server?

What other info do you need to have to help size the server?

Does it matter if the server has a 64 bit processor?

Speed of processor important? Speed of disks?

Thanks!