That is still a great workstation, and you can upgrade it nicely. Read this entire thread, and be happy you have been gifted a "revision 1" motherboard that has higher capabilities than the original motherboard.
Link is here.
Google Z600 QuickSpecs, and the top one will be about version 7 but the next one will be about version 51. Those reflect the original versus revision 1 motherboard.
The SSD I recommended in the above thread is the one to get. A fresh W7Pro64 is the way to go. You can upgrade processors, but if the Max TDP for the one(s) you want is over 95W then you need to make sure you have a "Perfomance" heatsink/fan over it. The search bar in this forum directs to this forum only. You'll need to spend some time. Note that you should only install a processor from the list in the QuickSpecs later versions to max out your performance, though you can use the older ones too.
These are still new enough and in demand..... two fastest "revision 1" category processors will not be cheap even used off eBay.