So, if your having difficultly installing an otherwise unsupported version of Windows, this table should come in handy for you. Credit to those to who know what program I made the spreadsheet in. Every version of Windows from 3.1 on supports some sort of high res/high color video driver within VirtualBox. I provided above which ones work in which version, you should be-able to Google around for the actual drivers, or PM me for a virtual floppy image for which version of Windows you need one for.
Networking is basically supported in every version of Windows, and should be-able to at least connect to a basic SMB/NetBIOS network, as long as it supports the protocol. In very old version of Windows that lack proper Networking support, you will need to install the DOS Networking drivers which are still available on a Microsoft FTP Server. You will then also need the PCNet3 DOS driver. I believe there is another forum post here about networking in DOS, just follow that guide.
Next, I'd like to mention the APM/ACPI support mentioned above. If you don't install the version of Windows correctly, you will notice it taking up large amounts of CPU cycles, even when idle. You will need to install the correct Power Management for whichever version you are using. To prove Windows 3.1 does indeed support APM, here's a screenshot:
Enabling it for Windows 95 is very easy, and APM is the default on 98, but ACPI is far better. APM isn't enabled by default on either 9x, and you will need to go into your Device Manager to enable the device properly. Be sure to force "APM 1.0", as I found that works best, especially in 98 which shipped with APM 1.2, and I don't believe it is fully compatible with VirtualBox's implementation of APM. For ACPI in 98, follow another guide on this forum, but if your 98 is already installed, then you may just have to deal with regular APM.
Finally, I'd like to mention the HDD column. The currently shipped guest OS templates won't auto-enable BusLogic SCSI for those guests, and furthermore, since NT 3.x requires an initial MS-DOS step of setup, you will need to swap the HDD controller after installation to enable SCSI on the system/boot drive. NT 4.0 and 2000 can use BusLogic SCSI out of the box from their bootable media, so VirtualBox should default to BusLogic SCSI for these guest systems. SCSI is less CPU intensive than IDE, so prefer it over IDE if you can.