Firstly you need to install Eclipse 3.5 Galileo, then once that’s up and running you can use the Spring update site to install the Spring Tool Suite (STS). Follow these simple step-by-step instructions. I’m assuming that you are the only Java developer using this machine.

1. Go to http://www.eclipse.org/downloads/
2. Follow the link for Eclipse IDE for Java EE Developers (189 MB) for Windows.
3. Select a mirror and download the file.
4. Create a folder called c:\java.
5. Move the Eclipse archive (eclipse-jee-galileo-win32.zip) into c:\java and extract here.
6. Folder c:\java\eclipse will be created.
7. Drag the executable eclipse.exe on to the desktop (or quick launch) and make a shortcut.
8. The workspace dialogue will pop up and ask you where you would like to keep your workspace. Spaces in file names (or directories) are always a bad idea especially when developing under a Windows environment which is why I don’t accept the default workspace location, so enter c:\java\workspace.

That was easy wasn’t it?. STS is now free so you can just install it from their update site.

1. Install Eclipse 3.5 Galileo mentioned above.
2. Open the preferences page Windows->Preferences.
3. Expand the Install/Update tree on the right hand side and select Available Software Sites.
4. Highlight all the Enabled sites and click Disable.
5. Click the Import button and enter http://dist.springsource.com/snapshot/TOOLS/sts-update-sites.xml. Eclipse spots this is a website then downloads and installs the xml. It may take a couple of seconds, but when it finishes click Ok.
6. From the file menu, go to Help->Install New Software….
7. Set Work with to AJDT - http://download.eclipse.org/tools/ajdt/35/dev/update. At the time of writing this there were no new updates so skip it and move to the next step.
8. Set Work with to Mylyn Extras - http://download.eclipse.org/tools/mylyn/update/extras.
9. Expand Mylyn Integration and check Mylyn Connector: JIRA, Next will become active to click it.
10. After a bit of rumbling (to work out dependencies which there are none) click Next.
11. Accept the License agreement and click Finish.
12. After installation you are asked to restart Eclipse, so click Yes.
13. Back into the Help->Install New Software….
14. Set Work with to Spring IDE Update Site - http://dist.springframework.org/snapshot/IDE/nightly.
15. Select all the components and click Next. More rumbling then click Next again. Accept the license and click Finish.
16. Back into the Help->Install New Software….
17. Set Work with to SpringSource dm Server Tools Update Site - http://dist.springsource.com/snapshot/DMS-TOOLS/nightly
18. Back into the Help->Install New Software….
19. Set Work with to SpringSource Tool Suite Update Site - http://dist.springsource.com/snapshot/STS/nightly/e3.4

Close down Eclipse and zip up the whole of c:\java\eclipse. Rename it to eclipse-3.5-sts.zip. If there is one thing I have learnt, it’s take a back up of a fixed working installation. Every one and his dog can write eclipse features and plugins. It is easy for one plugin to screw up another, so its really handy to have a “last known good position” to rollback to. Otherwise you may well find that you are going through this whole process again.

Original SpringSource instructions can be found here.