Recently i was stuck up in a place where i installed my VirtualBox ad Linux in windows xp. I tried pinging the Virtual linux from another win XP machine. But I was not able to do it.After a long googling found that there is a small tweak.
Go to Virtual Linux settings and check out for the network mode. There are different networks modes, change your network mode to bridged instead of NAT..
The reason you could't ping with NAT is because, this network mode assigns the virtual Linux a private IP and hecnce it cant be accessed from outsite.
Once you change that from NAT to Bridged you are all set.
Happy Virtualization :)
