- https://www.jetbrains.com/company/press/press-archive/pr_111... - press release for 3.0, Nov 11 2002
- https://www.jetbrains.com/company/press/press-archive/pr_021... - PR for 4.0, Feb 11, 2004
(Found via `intellij idea "3.0"` and `intellij idea "4.0"`)
- http://web.archive.org/web/20030320181401/http://www.intelli... - announcement for 2.6, Jun 3 2002
- http://web.archive.org/web/20030210115005/http://www.intelli... - APPROX - download page offering 3.0.1, archived Feb 10 2003
- http://web.archive.org/web/20010223163551/http://www.intelli... - APPROX - download page for 1.0.2 (build 339), archived Feb 23 2001
(Started poking around inside IA by following the EAP link at https://wiki.c2.com/?IntellijIdea, which is helpfully woefully out of date)
- https://confluence.jetbrains.com/display/IDEADEV/Home has info back to 9.x (expand "88 more" on the left)
- https://www.jetbrains.com/company/press/press-archive/pr_151... - irrelevant but interesting FOSS release announcement, Oct 15, 2009
If more accuracy is needed, perhaps the relevant info will only be one or intermediate pages away from the above.
I was trying to find out when these versions were released to see if I could line it up with the projects I was working on at the time, but I can't find a list of major releases with dates.