Birt Runtime Download
Below is the link for all the birt runtime versions starting from BIRT 2.2.2 to BIRT 4.2.1(latest) version :On below link select your required birt version and download birt-runtime-(your version here).zip package e.g.: birt-runtime-4_2_1.zip.
Birt Download page for all the version
Eclipse Plugin Link for BIRT
To install Birt report designer on eclipse go to Help>Install New Software and add link from below table for required BIRT Version.| Birt Report designer version BIRT 4.2.x  |  Eclipse Plugin link http://download.eclipse.org/birt/update-site/4.2  |  Description
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| BIRT 3.7.x (This Release Repo NOT available yet) | http://download.eclipse.org/birt/update-site/3.7 | 
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| BIRT 2.6.x | http://download.eclipse.org/birt/update-site/2.6 | 
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| BIRT 2.5.x | http://download.eclipse.org/birt/update-site/2.5 | 
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| BIRT 2.3.x | http://download.eclipse.org/birt/update-site/2.3 | 
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| BIRT 2.2.x   BIRT 2.1.x  |  http://download.eclipse.org/birt/update-site | BIRT 2.2.0/2.2.1/2.2.2/, 2.1.0/2.1.1/2.1.2/2.1.3 Release builds |