Well, I seem to have cracked the problem!
Here's what I did:
1) disabled Counterspy "Active Protection"
2) enabled scripts within Windows Media Player
3) deleted the MTV live skin, then re-downloaded it
The MTV live site now streams correctly. I still get the odd error message but on the whole I think my problem is more or less sorted for now
I think it MAY have been the Counterspy program that was creating the problem.
* An afterthought - if Windows Media player still plays up is there any way of checking whether the program has become corrupt? If so how would I go about correcting it? Oh, and do these so called "Registry Fixing" programs sort problems out or do they tend to make things worse? I had wondered whether to give one a try

I stay well away from the registry cos I don't know alot about it.