faeriemajikk,**
You can install almost any program on an external drive, period.
However I would recommend that you free some files on your main drive so that at least 5 GB is oper and it must remain open. Now you have enough space for a swop file if needed.
When you install to the external hard drive a couple of files (very little) will be installed to your C; drive but the majority will be on your external drive. Now Poser will work.

Please note that the above mentioned is my opinion and if other readers differ from me, keep in mind that every body is entitled to his/her own idiotic view. (Joke) I can not see why it will not work as a removable hard drive is nothing other than an extra hard drive.****
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Regards
Johan