Yes. You can install GuppY in a directory of your webspace. For example: www.mysite.com/guppy/

To acces GuppY in this directory, you will need to use the following url: http://www.mysite.com/guppy/index.php

Then there are no capacity constraints with GuppY, you can create as many contents as you want: news, articles, links, etc...

Therefore, in one webspace you could have several subsites, one installation of GuppY in a given directory, per subsite:
www.mysite.com/subsite1/
www.mysite.com/subsite2/
...
www.mysite.com/subsiteN/