Firstly, welcome aboard
So what kind of a PC are you running? Do you have the specs on it? Is the serial port that you're using a DB-25 or DB-9 type? If you mean DB-25 then very true, I doubt you'll find that on newer PC's. But DB-9's are still very common on desktops. Laptops are a different story and most now-a-days do not come with a serial port (at least not a DB-25 or DB-9 type). Now the good news is even if you do not have a serial port with a USB port you can get a USB to Serial (DB-9) adapter. The bad news is that I personally have had mixed results with those (hopefully others can chime in here on that point).
In terms of software...under Windows XP you can run in Compatability Mode. I've personally found few software products that run on 98 but not XP. Having said that, you are dealing with a medical company which from experience pays a lot of attention to the medical part of any device and very little attention to the PC end of things so it may not run as they claim on XP. What I would do is see if you can run it on another XP machine before you move forward...it may just work. For all we know the company may just be trying to sell you a new device.
You can definitely connect your older computer to a newer computer and gain varying degrees of accessability. There are many answers to that exact same question here on the board as well. Any number of people here on this board can help with that when the time comes and the solutions depend on what your setup is like now.
So what is the make/model of your glucose tester? How soon were you thinking of getting a new computer?
Casey