As long as you're running XP you won't notice any difference. There have been many tests over the years which verified this. You'll have to look way back in the archives (4-6 years), but Tom's Hardware Guide, Anandtech, Ars Technica, and Bjorn's 3D websites have all tested XP performance with varying amounts of RAM and concluded that the sweetspot for XP was 2 gigs.
Back when the tests were conducted RAM was considerably more expensive, and most systems shipped with only 128-256megs. At that time they found that anything above 512megs the price to performance ratio went down dramatically, but that there was a definite performance increase until 2gigs. After 2 gigs there was no noticeable performance increase in either the benchmarks or "real world" XP usage.
If anyone doesn't believe me and wants to check for themselves there is a simple way to confirm without running extensive test suites. Just use the "three finger salute" (control-alt-delete) and bring up the "Task Manager", click on the performance tab and run whatever programs you would normally. The 2 lower graphs illustrate how much memory is being paged to the swap file. With 2 gigs you'll notice that the line is pretty much flat and only varies with a large number of applications and windows open. And even then the variance is only a small amount. The only exceptions being when manipulating extremely large files in those applications.
In any event 32bit Windows of any flavor doesn't recognize over 3gigs so any RAM above that amount is wasted.
On the other hand you have an E1705 that when partnered to the right Core2Duo processor is capable of running a 64bit OS. 64bit OSes will use and take advantage of all the RAM you can throw them. Something to think about.....
I hope this helps.
Ciao
