RAM configuration

I juste upgraded the RAM on my MacBook (1st Gen) from 1 gig to 2 gigs.

I'm running Parallels 2.5 (build 3188).

In the parallels "Memory" preference pane, the automatic "Adjust reserved memory" value is 512 MB. I don't think it has changed since the RAM upgrade.

Should I increase the value? To what?

Same question for my Windows XP VM.

Instinctively, I want to double the memory allocation in both places.

TIA for your insights.