Welcome to the Apple discussions.
Here's why I would proceed cautiously on that deal.
First, the memory they offer, Kingston Valueram, typically does not work in Powerbooks. It's in a class of memory that meets the printed PC2700 or PC4200 specification, however, doesn't work well with Apple's architecture. Kingston offers a standard line of RAM which works just fine, and would be recommended.
Second, the 3 year warranty is with one of their retail affiliates, which could mean anyone, which puts it into the class of any exteneded warranty...it's only as good as the company fulfilling it. With Apple's extended warranty, not only do you get the additional 2 years of hardware coverage, you also get 2 years and 9 months of telephone coverage. This can be especially helpful if you're new to macs and mac software.
If you're really hungry for this deal, the first question I'd ask is whether they are an Apple Authorized seller, and I might ask Apple that question. If they are not, then Apple may not stand behind their standard warranty.
You might consider an Apple refurbished unit, for a lower price (on the Apple store site, click on 'save' in the bottom right hand corner. Currently 20%-40% off list on 17" PB's). Also, Apple has some good educational discounts, and your employer might have a discount program with Apple too.