Hi!
It showed up to be much easier than it looked like at the beginning.
So, step by step:
1. You have to install 32 bit compatibility libs available at [url]http://connie.slackware.com/~alien/multilib/[/url];
2. IASL compiler, available at [url]http://www.acpica.org/[/url]
3. Make shure your kernel tree is up-to-date (usualy under /usr/src/linux); in my case it was necessary to re-build it because afterwards I was not able to to make a VBox kernel module;
4. O, yes - you must download VBox OSE source, VirtualBox GuestAdditions iso file and manual if you want the full package having everything;
5. After that you can use VBox build script available at [url]www.slackbuilds.org[/url], it is necessary to correct the architecture form i486 to x86_64.
It could be necessary to tune the build script a little (for example - if you do not want the manual to be included in packaged).
If evereything is ok, process will end giving ~60 MB tgz
two small philosophical P.S., not related to building of package:
1. I can't understand, why it is absolutely necessary to have internet connection for the first use of vbox just to register it and why it can not wait until connection shows up (i had a problem with it some time ago when due to the lack of internet connection i was not able to use it at all);
2. If the OSE is stripped down version of VBox, why registration is not voluntary, like for example, OpenOffice, but obligatory, plus see (P.S. #1)

