I get:

$ ./boinc_client --attach_project http://setiathome.berkeley.edu $ACCOUNT_KEY
23-Aug-2008 22:36:38 [---] Starting BOINC client version 5.10.45 for i386-unknown-openbsd
23-Aug-2008 22:36:38 [---] log flags: task, file_xfer, sched_ops
23-Aug-2008 22:36:38 [---] Libraries: libcurl/7.18.0 OpenSSL/0.9.7g zlib/1.2.3
23-Aug-2008 22:36:38 [---] Data directory: /opt/boinc
23-Aug-2008 22:36:38 [---] Processor: 1 i386 Intel Pentium III ("GenuineIntel" 686-class)
23-Aug-2008 22:36:38 [---] Processor features:
23-Aug-2008 22:36:38 [---] OS: OpenBSD: 4.3
23-Aug-2008 22:36:38 [---] Memory: 510.46 MB physical, 512.34 MB virtual
23-Aug-2008 22:36:38 [---] Disk: 6.27 GB total, 4.35 GB free
23-Aug-2008 22:36:38 [---] Local time is UTC +2 hours
23-Aug-2008 22:36:38 [http://setiathome.berkeley.edu/] URL: http://setiathome.berkeley.edu/; Computer ID: not assigned yet; location: (none); project prefs: default
23-Aug-2008 22:36:38 [---] No general preferences found - using BOINC defaults
23-Aug-2008 22:36:38 [---] Preferences limit memory usage when active to 255.23MB
23-Aug-2008 22:36:38 [---] Preferences limit memory usage when idle to 459.42MB
23-Aug-2008 22:36:38 [---] Preferences limit disk usage to 3.14GB
23-Aug-2008 22:36:44 [http://setiathome.berkeley.edu/] Master file download succeeded
23-Aug-2008 22:36:49 [http://setiathome.berkeley.edu/] Sending scheduler request: Project initialization. Requesting 1 seconds of work, reporting 0 completed tasks
23-Aug-2008 22:36:54 [SETI@home] Scheduler request succeeded: got 0 new tasks
23-Aug-2008 22:36:54 [SETI@home] Message from server: platform 'i386-unknown-openbsd' not found
23-Aug-2008 22:36:54 [SETI@home] New host venue: home

Then nothing more happens. The boinc_client is just sleeping. Is there any solution to this?

There is a problem with your installation. The BOINC client has not found a manual installation of the app_info.xml and the OpenBSD SETi application. Have you installed the SETI@home application, too ? - A SETI@home and Astropulse application is available at my homepage www.dotsch.de/seti.

If you have installed the SETI application manualy, could you please verify, if in /opt/boinc/projects/setiathome.berkeley.edu the files app_info.xml and setiathome-5.27...
If the files exists, stop the BOINC client and start it again with "./boinc_client --update_prefs http://setiathome.berkeley.edu"

If you have installed the SETI application manualy, could you please verify, if in /opt/boinc/projects/setiathome.berkeley.edu the files app_info.xml and setiathome-5.27...
If the files exists, stop the BOINC client and start it again with "./boinc_client --update_prefs http://setiathome.berkeley.edu"

Thanks for the reply!

It appears to be working now, the app uses preferred cpu% settings.

If someone else has the same problem I did, you could try:
1 $./boinc_client --detach_project http://setiathome.berkeley.edu/ #this command removed the files in the project directory

2 download and $tar zxvfp seti_boinc-5.27.00-openbsd-i386.tar.gz #because the needed project files were gone due to the previous action

3 $./boinc_client --attach_project http://setiathome.berkeley.edu $ACCOUNT_KEY #hit CTRL-C and continue with:

4 $./boinc_client --update_prefs http://setiathome.berkeley.edu

# sometimes the SETI cpu% settings seems to be forgotten by the application. The strange thing is that it doesn't always happen. Maybe I'm just too tired...

Cheers!