Can mIRC be installed on and run from a USB memory key or USB harddrive?

So long as the key/hard drive has sufficient room and connectivity, I can't see why not. While I don't have mIRC running from a USB drive, I do have it on a parallel port drive on one system, and it works fine, taking into account the fact that the parallel port drive doesn't have the same access speed as the hard drive does.

I agree with RusselB, recently one friend of mine is running mIRC by a Flash harddrive, and he dont report me any problem! the only thing i think its not soo good is the low speed of processing of mIRC runing on that!

Thats all

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When running mIRC on a USB Key, keep in mind that flash drives have a limited lifespan of write access (they die after about 1000-10,000 writes or so, which is a considerably short lifespan).

Avoid using scripts that perform many reads/writes, and consider turning logging off or have logging directed to your primary harddrive. This will help assure the longevity of your flash drive.