I dont think there is anything wrong with the RAW converter in PSP. The CA(purple fringing) must have been in the picture to begin with. Nikon cameras has a built in automatic CA correction when it creates its jpgs. I dont think you will get a better result with any other Raw converters besides Nikon's own NX2 which probably has that CA correction built in too. However, you should be able to correct for CA in PSP. I used to use PSP and I really enjoyed using it. Its auto photo corrections worked great(and can be tweeked) and its clarify(is that what its called?) function was invaluable.
I use Linux these days. I mainly use TheGimp and plan to get bibble pro 5 or bibble lite soon which is very similar to lightroom. TheGimp is great fun but a bit "different" and quirky and takes a bit of getting used to. You will need a bit of grunt(PC GHZ) to run it on windows. However, if you persevere you get the advantage of getting some very nice free plugins to do just about anything .. if you can find them which is a bit of "fun" too..(read hassle if you are not a hacker) however the base install of gimp has more than what most people will need.
New gimp (2.8) is expected at the end of the year. It will have a whole new UI that is much nicer and a whole bunch of improvements in speed and modularity as they are changing over to a new graphics library. Which can fully use all the multi cores of the new CPUs... All very exciting to an old hacker like me.