Hi, Joe.
Unfortunately, you're out of luck. Your only lawful choice — given that you don't want to pursue the alternatives, e.g. VirtualPC, etc. — is to purchase legal downloads of the same content in Mac-compatible formats, if available.
You wrote:

'Its seems to me a real shame that apple and microsoft can't once and for all work this thing out.'

That's unlikely to happen. Each firms' DRM technology enforces a strategy of locking you in to their platforms: Windows DRM to Windows, Apple's FairPlay to iPod and iTMS. There is no economic incentive for them to make their DRM formats compatible with the others' players as that makes it easier for you to switch platforms without incurring potentially substantial switching costs. To understand lock-in and switching costs as competitive strategies, I recommend the book Information Rules by Shapiro and Varian.
For example, if the WMVs in question were legal downloads you purchased, you're now faced with the following switching costs: you either (a) lose the use of those files (meaning the money spent on them originally is now wasted), or (b) re-purchase the same content, if available, in a format that is Mac-compatible.
One of the incentives Microsoft has proposed to get iPod users to switch to Zune is that they will make iPod owners 'whole' with respect to their iTMS purchases. That's an expensive switching cost and an unusual technique, revealing how desperate MS is to have iPod owners switch to Zune.
You wrote:

'So much content is now being protected to prevent copywright infingement which I understand, but it also means that access is becoming more and more limited to us mac users.'

If it weren't for piracy, there'd be no need for DRM. Rampant piracy has forced the owners of intellectual property to resort to DRM to protect their rights. Therefore, the real blame goes to the pirates.
Good luck!
😉 Dr. Smoke
Author: Troubleshooting Mac® OS X