To install Eclipse IMP for the first time:
Note: Some of the screenshots used in these instructions are out
of date in that they stilll refer to IMP as "SAFARI." The name
will be changed to protect the innocent; in the meantime, if you can
pretend that SAFARI really means IMP, these instructions should still
be good.
- From Eclipse, invoke "Help" => "Software Updates" =>
"Find and Install"

- In the dialog that shows up, select "Search for new features to
install" and click "Next"

- The first page of the "Install" dialog will appear; click
on the "New Remote Site" button on the upper right-hand side of the
that dialog ...

- The "New Update Site" dialog will appear
- In the "Name" field type "IMP"
(this can be anything you want, it's your name for the update site).
- In the "URL" field type
"http://eclipse-imp.sourceforge.net/updates/" (note the
trailing '/' character;
it's significant)
- Click "OK"

- This will return you to the "Install" dialog, where the IMP site
will be added to the list of sites available for searching; be sure
that the IMP box is checked and click "Finish"

- This will bring up the "Updates--Search Results" page; check the
"IMP" checkbox, making sure you're getting the latest version, and
click "Next"
- On the "Search Results" page, check the "IMP" checkbox,
and
click "Next"
- Click "I accept the terms..." and Click "Next"
- Click "Finish"; the dialog will disappear, and the status
bar
will show progress as the Update Manager queries the update server for
all available updates
- Click "Install All"
- Click "Yes" when asked whether to restart Eclipse (assuming that
you are done with updates and ready to begin working with IMP)
The IMP installation includes IDEs for X10 and the LPG grammar
specification language, so you should now be able to see syntax
highlighting, an outline view, and other IDE features
when editing .x10 or .g source files.