Wow that is a tough question. Money plays a big part here and as always the more you pay the more you get.
Firstly though, Have you tried searching for updated drivers for your old midi interface? It could just be drivers that are the problem.
Now for some midi programs that I have used:
FL Studio :: starts from as low as $49 with studio express edition. There is a free trial and they provide free updates for life. I have the fruity edition and while it is great for midi I no longer use it as I am now more recording focused and use a strong daw with specialised midi plugins to achieve what I am after.
Mixcraft :: $74.95 This is a great recording program with built in midi control and the ability to handle plugins. Comes with a library of wav loops and there are thousands of free vst instruments and effects plugins available on the web. This is a robust program and can handle most users requirements.
Cubase : $$$ This is now my daw of choice. It is fantastic to use, never crashes and has great midi capabilities. Some of their specialised plugins ie HALion Sonic provide more featurs and sounds that you could ever hope to explore.
Of course you are also going to need a controller or keyboard to connect with and that is probably the best place to start looking as they often come packaged with software. I only use a 49 key keyboard controller and for my needs it gets the job done. Mine is an M-Audio keyrig 49 and it connects via usb and I have never had a problem with it. I was not interested in M-Audio's software, its probably good, but I didnt want to go through another learning curve and it was only bundled with entry level versions anyway. The controller only really acts as a way to get the signal into your program in a tactile way IMHO so I beleive in buying a cheapish controller and concentrating on the software for the real investment in getting top draw sounds and expressions.
Hope that rambling helps a little Phil, if not it may serve as a good introduction to someone who is thinking about midi.
As always I hope you enjoy my musical journey as much as I do.