I don't mess with VirtualPC much because I prefer to use VMware as it is much easier to configure and FASTER.... plus it is FREE (the player version).... so I can't help you here really except to suggest you to try VMware Player
VMware clients allow 3 different types of network connectivity... bridged, NAT, or host-only... all easily configurable from within each guest's settings
VMware also allows advanced customization, such as modified BIOS ROMs, host SCSI port redirection, etc

you can easily convert to/from a virtual PC image to a VMware one

if you use VMware workstation, it even allows fine tune of the VMware network adapters installed on the host system

I now use VirtualBox exclusively after using Virtual PC until the Windows 7 version was released. It was very poor at networking in particular that I got fed up and binned it 😀 My advice, take a copy of the VHD and load it into VirtualBox directly and see if it's better. VMWare is also a good option though I prefer VB for home and ESX/VSphere at work 😀

Does your DB server need to accessible on your network or just from the VM host machine? I run a few servers for testing purposes and run the Virtualbox network in NAT mode. Each machine can see the Internet but don't allow access in except from the host on certain ports. The guest has a few NAT rules configured (port 8080 for example) by way of the vbvoxmanage modifyvm command. I add a local entry in my hosts file if I need to access the machine via name. For example, a test TFS server is running on a guest. From my Visual Studio client I simply add the TFS server by name and if the guest is running the Team Explorer component will connect to the server via the port redirection.

There are a number of options open to you using VirtualBox: http://www.virtualbox.org/manual/ch06.html

I like VMware over VirtualBox because it's more easier to configure and customize... but VirtualBox works better with retro OS's and it has a "real" SB16 emulation... I used it to test the real SB16 drivers install disks, and they worked!

I only use VirtualBox to run XP, for the occassional Microsoft Sam, and testing of fishy suspicious programs that may contain nagware (like every modern shareware).

I do use Virtual PC for networking though 😜

When I virtualize Windows 98 SE on VirtualBox, the VBox Additions are unable to be installed.
I installed the x86 one. I setup ICH9 for Northbridge and some old hardware to a bear minimum My vbox 4.1.8

Any help would be greatly appreciated!
Thanks
Jack

use vmware player 3.1.5... it will have those guest OS additions you need (virtualpc might too)
virtualbox does not have them and I don't think it ever will