The real trick is ensuring that application functionality and familiarity remain intact. I believe there is such a tool that will allow this to happen indeed, it has worked well for many computing environments already.
One approach: run Windows software off of the Windows server while allowing the end user the freedom to use older hardware running a thin client called Thinstation. Taking this approach means both access to full fledged Windows software while enjoying the ability to utilize old hardware dragged up from the basement as a client machine.
Sometimes taking a thin client approach is not of value, at least not in all circumstances. Sometimes you find that you have workstations that are older, not connected to the network, but still could be used with software upgrades.
This may be a situation where older workstations running Windows 2000 Pro are in use, but are not of value to the company due to budget restrictions that mean no new software purchases for these older PCs. This is not a problem. Just look to Free Software/Open Source for some assistance locating applications that might enable you to get some more life out of the now dated PC.
Often using various open source software applications that are available, though not able to be run natively in a Windows environment, will more than fit the bill for the needs of these old workstation PCs. Assuming the abilities of the software can match the abilities of the workstation hardware, most open source applications run on all semi-recent versions of Windows.
So what types of software can be used on an existing XP box from the open source archives? Generally speaking, everything from Web browsers to office suites. Some favorites include:
You get the idea...
As you can see, there are a number of applications that open source software can lend a helping hand with. Unfortunately, it is not a panacea for everything that a company needs from a modern workstation. Sometimes, those pesky legacy apps can get the best of us, no matter how hard we might try to embrace something with a more liberal license going for it.
When closed source software remains a legacy need
Now many businesses face the reality that closed source software will remain part of the company despite any desired open source migration ambitions. Whether it be some legacy application that is simply not available in an open source alternative format or even if the existing open source alternative just is not measuring up.
In either case, sometimes there is just no escaping it. Even with the desire to keep things in an open source atmosphere, often it proves to be more cost effective to simply bite the bullet and stick with the legacy application.
That said, I would point out the inherent danger when using closed source software with any level of long term reliance. For an example, grab a document made with Microsoft Publisher 2002 and attempt to open it with Publisher 2000.
That's right, it wont open.
That type of vendor lock-in is my biggest issue with proprietary software and the document formats they often support. The moral of that story is to avoid using proprietary applications whenever possible, but to remain flexible to using them if nothing else will do. It's an unfortunate reality, to say the least.
At the end of the day, it may be a necessary evil, but if there are open source alternatives, be sure to exhaust attempts to switch to them completely before tossing in the towel.