An old PA-RISC wont cost you much (100-200 $ ) the same is true for SPARC... I gave away some of my sparcs because I had no room... For an AIX or HP-UX, be sure you have a system with OS installed...

Although it's reachable from drl's link, the best reference for NetBSD platform support is probably http://www.netbsd.org/ports/

For OpenBSD, see http://openbsd.org/plat.html

Regards,
Alister

Thank you very much. Indeed, i'm relieved : i was thinking that it would be expensive to find any older adequate hardware.

I suppose you warn about OS installed due to any first installation difficulties ?

Thank you.

---------- Post updated at 04:10 PM ---------- Previous update was at 04:09 PM ----------

Thank you

No, Its more that the software costs $$$ you wont be able to find the install CDs like that and many are keyword protected...
If you were living in Geneva, Switzerland, kindly asked, I would have given you a HP A400 or a D270 and a sunblade 2000...

If you are willing to try one of the BSD flavors, then you might want to check out GhostBSD, which has a live version, so nothing gets installed on the hard drive and you will quickly find out whether FreeBSD is something for you at no extra hardware cost.
Having said that, I find that there are large differences between Solaris and FreeBSD.