Sure. The IntelliGanttWebPart2007.wsp is a 'Windows Solution Package' designed to install on a SharePoint 2007 (WSS or MOSS) server. It can be a standalone server or a farm.
You use STSADM.exe to perform the actual installation steps:
1) Add the solution
example: C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN>stsadm -o addsolution -filename intelliganttwebpart2007.wsp
2) Deploy the solution
example: C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN>stsadm -o deploysolution -name intelliganttwebpart2007.wsp -allcontenturls -allowgacdeployment –immediate
Once the solution has been added and deployed, then you will see the 'IntelliGantt Web Part' as an activate feature in the Site Collection Features page. You should also see the IntelliGantt Web Part in the web part gallery. Finally, when you wish to add this web part to a SharePoint page, it should be grouped in the Project Management category.
However, if you are using a 3rd party hosting WSS, you most likely will not have access to the necessary STSADM tool. In this case, you can still use the IntelliGantt Web Part by uploading a file to a document list and referencing it in a Content Editor. It's a little involved, but doable.Here are the detailed steps for that procedure