Could be a virus, but I'm not thinking so.
Your processor is faster than that of my laptop and I downloaded and installed Windows 7 RC just fine. That would not affect your ability to obtain the OS.
When you say 2.50GB of physical memory are you talking about your hard drive or your RAM?
If this really is your hard disk space, then you cannot download Windows 7. The cd image file is over 2GB in size for any of the versions and Vista takes over 1GB itself.
To verify this, look under Start > Computer
Your hard disk drive(s) should be listed at the top including the amount(s) of free space.