I created a BOOT.INI file in C:\ with your suggested content but nothing changed.
Is there other resolve way to dual booting Windows7 with OpenBSD?
Well, IF the BOOTMGR boots, THEN it will parse the contents of BOOT.INI, i.e. at least you should have an added entry in the boot menu for "My nice OpenBSD", of course the file C:\boot\openbsd.pbr needs to exist and it needs to be a copy of a valid PBR to go further.
Try adding to the root of the C: a grldr from grub4dos and add to boot.ini a line:
You should now have two added choices at boot time, one "My nice OpenBSD" and one "grub4dos", and if you choose the latter you should get to the grub4dos prompt.
Is it not that you are using a UEFI (as opposed to BIOS) machine?
How EXACTLY did you create the openbsd.pbr file?
Are you sure you have an A6 type partition?
Since it is not the first time that I have to apply (light) forms of torture to wring from you the needed basic info that you should have posted on first instance, it would be nice if you could provide the Standard Litany:
"it doesn't work", "nothing changed", etc. do not provide enough info to help understand what may be the issue, try describing what you did, and what is actually happening