There is no tool that can convert VMware images directly to VirtualBox vdi format without having to do a dump/restore over ssh or something similar, but qemu-img can convert .vmdk VMware images to raw format, and those can be converted to VirtualBox .vdi using vditool.
First, make sure you have qemu installed, and have downloaded vditool.
- Convert the VMware image to raw format:
# qemu-img convert -f vmdk VMwareImage.vmdk -O raw RawImage.img
- Convert the RAW image to vdi format.
# vditool DD Image.vdi RawImage.img
Now start up VirtualBox and associate the .vdi image to a new virtual machine. You may need to change the bootloader settings for the OS (disk changes and such).