I am having strange problems with my mouse. when I use the middle mouse button to rotate an object in the 3D window sometimes it works then the next click it wont. If I go down to the header and hold down the middle mouse button occasionally I can get it working again but usually I have to go to a outside program then middle mouse click and pop back in to blender to rotate the view. I have tried 3 different mice and they all do the same thing. 2 Microsoft cordless and 1 logitech cordless mouse. I am using blender 2.45 on windows xp pentium 4 3gh hyperthreding computer with 512 mg ram. I have resorted to using the keypad to rotate. 
Well I have been searching the web, reading everything I can find that says rotation problem and could not find anyone having the same problem. It must be something on my system. Well I looked through all the menus and found in the user preferences window under view and control a button that says emulate 3 button mouse. so I tried it out. Now if I use the ALT+LMB it replaces the MMB in the 3D view. Actually I think it is easier to rotate the view this way than with the MMB anyway. I still would like to know if anyone has a clue what would make the MMB work intermittently. I haven’t had problems in any other program.
I’ve experienced this a couple times recently. Haven’t been able to reproduce it intentionally however.
I found the solution. It was the Nvidia card. I set it back to factory default and everything is fine now.
Jimtuv- Thanks for the posts! I’m a Blender newbie, struggling with a similar problem on a Dell Optiplex 745 running Vista Ultimate. I installed Blender 2.45 about a month and a half ago, and 2.46 just now, on this, and also on an older XP machine. On the XP, the MMB works fine for rotating and panning, but on the Vista, it does nothing at all, and the scroll wheel for zooming only works sporadically. Otherwise, everything seems fine. Not being able to rotate or pan the view has been extremely frustrating, and I thought I’d have to fall back on the XP (which has quirky problems of its own). Following your 09-Mar-08 post, I tried Alt-LMB in place of MMB, and found it works, on both machines. I am ecstatic!
I suppose my MMB failure is a driver problem. I have a 256 MB ATI Radeon X1300PRO for the display adapter and an HID-compliant mouse, but Windows tells me the software for them is up to date.
Again, thank you very much for your posts. They really helped me. 
Its definatly a mouse driver problem. Dont believe windows when it claims a driver is up to date… they almost never are. Check yourself using google.
How did you set it back to factory default? I have the same issue and really need it resolved.
Uninstall the SetPoint tool from your Vista PC.
Then you will not be able to zoom up/down desktop and ie7, but you will be able to rotate and pan 3D views with middle mouse button! 
You know what, I just plugged in my spare mouse and it works now. Must be something to do with the Dell mouse.
May be your Dell mouse is same thing as Logicool’s one that uses the SetPoint tool. But your spare mouse is not and don’t use it.
AHA!!! In the bottom right of my desktop, in the running applications icons next to my clock, there is a Mouse Suite icon!
I ran this and there is an option to change the scroll wheel to Auto Scroll instead of Zoom!!
Woot! happy days!
is really useful for me, I am glad to read it here.