RAM:
4GB is always better than 2GB

However, 2GB is a lot already, and if you don't use a Virtual Machine or process huge files sometimes you won't notice a difference.
Win 7:
The upgrade to Win 7 is advisable, it's not only faster, but also more tablet PC optimized. It has a much better TIP and other features which makes it a joy to use on a tablet PC with the pen. Also does it work better with SSDs than Vista.
If you do the upgrade and also install 4GB of RAM, then you can also think about using Win 7 64bit. This will allow you to address the full 4GB of RAM, and if you use some 64bit optimized software, like PS CS4 64bit, you'll also notice a speed improvement.
Though, Fujitsu does not fully support the 64bit OS yet, this means that some rare Fujitsu specific tools won't work, e.g. Security Panel. It works regardless what OS you use, but you can't change the code in a 64bit OS, you'll need a 32bit OS for this.
SSD:
The speed improvement will be noticeable at boot up or first start of programs, but with 4GB of RAM, Win 7 and the improved SuperFetch, and the use of sleep mode, the difference will be really small in normal use again.
A good 160GB SSD is really expensive at the moment. If you don't need more space and have enough money to buy one, then why shouldn't you use it. However, I couldn't live with just 160GB, also is the speed difference not worth the money in my opinion. Better get a 500GB HDD for much less money.
Software:
Well, there are a lot of useful tools for a tablet PC. Sadly does every software has its quirks.
Larger software worth a look:
Microsoft Journal, Microsoft InkSeine, Microsoft OneNote, Evernote, Bluebeam PDF Revu, Grahl PDF Annotator.
Inkseine is great for brainstorming, Journal and OneNote for heavy notetaking (both have their advantages and disadvantages), Evernote for casual notes (as far as I remember isn't it possible to mix ink with text), PDF Revu as PDF viewer/annotator/editor and with some tricks note taking program, PDF Annotator for normal PDF annotating.
Just try every software and find the best mix for you.
I used ON in the past, but stopped using it because the bugs made me crazy and I wasn't able to do the stuff I needed. The same with Journal, just not enough features.
InkSeine, I liked the ideas, the lack of features made it useless for me.
PDF Annotator, a small and simple tool, sadly not usable for me and it did not work as I liked, finally I only use PDF Revu at the moment, and if Bluebeam keeps improving it as they do at the moment, I won't stop using it.
I keep all my files in PDF format, so everyone is able to read it, I have good print outs and it's easy to keep everything organized. However, it's perfect for my needs, others may prefer Journal or other tools.
There are also tons of little tools which may be interesting for you, like
TEO, several OneNote PowerToys, other tools mentioned in the Software area.
You may also want a useful calculator, so either take a simulated TI, HP or other calculator, or, which I use,
XCalc which uses RPN, just the best notation
