Did you try building the virtualbox guest services yet?
When you run the slackware guest OS, In the upper right hand corner click "devices > Enable guest additions".
After that, if you aren't already in a x11-windows (kde, xfce), you should see the following show up in dmesg :
[ 6052.706909] ISO 9660 Extensions: Microsoft Joliet Level 3
[ 6052.732052] ISO 9660 Extensions: RRIP_1991A
And, you should see the VBoxGuest additions automajically mounted from /dev/sr0:
/dev/sr0 on /media/VBOXADDITIONS_4.1.16_78094 type iso9660 (ro,nosuid,nodev,uhelper=hal,uid=1000)
If it isn't automajically mounted, you may have to mount it yourself:
root@solarisvm:~# mount /dev/sr0 /mnt/dvd
At which point you should see the contents of the iso in your mounted directory.
cd into the iso directory, and then run (as root):
You may need to run the "runasroot.sh" script, although if I remember correctly that didn't work for me in slack. Try running the VBoxLinuxAdditions.run first. After that completes, go ahead and reboot. If it was succesfull, you should see the following kernel modules:
root@solarisvm:/media/VBOXADDITIONS_4.1.16_78094# lsmod | grep vbox
vboxvideo 1129 1
drm 143170 2 vboxvideo
vboxsf 34567 2
vboxguest 151850 6 vboxsf
If you see that, then you are all good! Just go to the GUI in the vm "Devices > Shared folders" to define your shared mounts. After that, you can mount your shared mounts by using the following command (immagine you named your shared folder mydocs, and you are mounting it to /mydocs):
/sbin/mount.vboxsf mydocs /mydocs
And if you're succesful, you should see the following
mydocs on /mydocs type vboxsf (rw)
Note: if you read the virtualbox directions, it'll mention you need to install DKMS first. This isn't trully neccessary, unless you plan on upgrading the version of guest services you're running. Which honestly, can be done by hand, you'll just have to remove the current vbox modules first.
Hope this helps! Note: I'm running winxp as host os (on my work system, where win is mandatory
Another good reason for the guest additions, is it exposes the hardware to the guestos. You can resize the VM resolution on the fly, and it'll accept whatever resolution is running on your native host.