How much of an improvement will I see?

[coachingguy]

I've got a 17" iMac G5 2.0, 150 gig(?) HD that I'm replacing with a refurb'd 20" 2.4 Duo 2 250gig 7200.

I'm just wondering how much of an improvement I'll notice. The G5 has 1.5 gig ram, the new (to me) 20" will arrive with 1gig, but I've already ordered the 4 gig upgrade.

Also, I've got a 2.4 MBP 15" with 2gigs, how will the new iMac compare to the MBP?

Thanks in advance.

Coachingguy