I still run a number of applications at work that need a serial port, ranging from virtually new Win7 compatible applications to an old (20+ years old) DOS program. That DOS program runs fine under the Windows XP command prompt (even under XP Mode in Win7). It even runs under DOSBox (although I've not used it that way, and if I did I wouldn't be asking for support as its not a game). Anyway, using these applications in recent years means I've had to use USB to Serial adapters as the ports vanished from laptop PCs, and my colleagues and I have found the best USB adapters are, bizzarrely, the cheapest ones! Some of the high end adapters have too many features and use fancy drivers that get in the way of 'simple' programs. The cheap ones, however, use very basic drivers to emulate a hardware serial port. Better still, the cheap ports also allow the port number to be changed in device manager meaning it can be set to a DOS application friendly number (the DOS application I use only works with COM1!). We've used the cheap blue Startech adapter in the past with no problems, and that costs less than Â£10 in the UK. Provided your program accesses the port via conventional means it should work with one of these cheaper ports. However, the usual caveats apply. This is just my experience and I do not offer any guarantee it will work for you.....try it at your own risk.....don't blame me if it doesn't work etc. Good luck, and any chance of telling us what your program is? As has been said Dosbox is not ideal for non-games and there might be a better solution. For example, I have Oracle VirtualBox running 'real' MSDos 6.2 quite happily. I've even managed to get the upper memory going, along with a Sound Blaster DOS driver and Windows 3.11 complete with TCP/IP networking to the Windows 7 host. But I still go back to DOSbox for Day Of The Tentacle because there it works perfectly!