The difference is not much accept that the dv1000t is a slightly advanced CTO notebook, but the dv1xxxx series are very alike in many ways, mainly look.
No, the video card is integrated into the mother board. There are ram upgerdes available though.
Main system (mother board) drivers (sound, video etc) can be downloaded from HP's website, usually found in the support area under downloads. Accessory drivers can be downloaded from Drivers.com, usually found by the driver or manufacture type I.E.: Nivida video card, Soundblaster sound card. They will ask for the card model number and then the system will provide you with the most up to date drivers for that card.
Winnt 4 is an obsolete network operating system (NOS) from the Microsoft corp. in the early 90's . It's very limited and premitive in function and supports. It does not support for USB or even wireless. So don't even bother to install WinNT 4. It's better to use WinXP with SP2 to get support for wireless. Also new Vista OS also supports wireless.
On a computer with both Windows Vista and either Windows XP or Windows Server 2003 installed, Windows XP or Windows Server 2003 deletes any existing System Restore points belonging to Windows Vista during boot. Microsoft confirms this issue but maintains that it is a fundamental function of the way XP works and cannot be changed. According to Microsoft, the solution is to install Windows Vista on a separate partition invisible to XP.