Your machine is a bit light, but should work for basic samples. You won't be able to run gigs with GigaPulse built-in - especially pianos that use the pedal to select ambience. And you won't be able to run the latest deeply sampled pianos with only 512 MB of RAM.
GigaPulse 3.2 is touted to have a big performance gain on 24-bit samples, so you should be able to run 24-bit libs okay.
GS3 includes iMIDI features like legato, round robin and the DEF filter. These might be problematic. The DEF uses processing power, so that's probably out. Round robin will probably work, but you might get some clicks, if the machine can't keep up.
I guess the bottom line is that on your PC you should be able to use GS3 at the level at which you've been using GS2.5, but you won't be able to use any of the new features, aside from 24-bit library support.
Note: A 2.4 GHz Pentium is the minimum hardware recommended for playing the GigaPulse-enhanced GigaPiano.
Best of luck with your software upgrade - and any hardware upgrade that you might be planning.
It seems that the memory bug is only affecting people with 2GB or RAM. Giga has generally been able to access most of the RAM from 1GB and smaller systems. It's only on larger memory systems that the RAM tweak has been required, and that seems to be the area for this new issue.
For this system, I'd go for 3.2, considering the boost in 24-bit performance - which will be very helpful on a 1GHz processor.