it sounds like a permissions issue. what plugin are you trying to install?
try setting the permissions to 755 for the section/directory you're plugin is being imported to. you should be able to open the zip file for the plugin and read the .xml file to see where it is trying to install.
Thanks a lot. That fixed the error, but now it's saying that the folder is already being used and it can't be overwritten. Does that mean I have to uninstall the older version of the extension in order to install the newer version?
I tried deleting the directory, but it still gave me the error that it was being used. Then my brilliant self (it comes and goes) decided to look at Extensions --> Install/Uninstall --> Components and uninstalled the old version. The new version installed without a hitch after that and works beautifully. Thanks for all the advice