how to open and modify eps with gimp
If I understand this bug report (https://bugzilla.gnome.org/show_bug.cgi?id=689657) correctly, you can check if your version of Gimp supports ps and eps (it may not, even if you have ghostscript) by doing the following:

Open Gimp.
In the menu, click help, and then procedure browser.
In the procedure browser search for 'file-ps-load'. If it's not listed, Gimp won't open ps or eps files.

My version of Gimp doesn't have this. But I haven't tried downloading the current version, maybe the current version has this enabled.

It's not too hard these days to set up Linux in VirtualBox. If you have no other alternatives available and don't want to buy Windows or another computer, you can use Gimp on Linux (probably Ubuntu) in VirtualBox.