Which Drivers do I need for Vista & where can I get them ?

I have a Dell Optiplex GX 620 System that came with Win XP PRO SP2.

I want to install Vista ( Ultimate ) 32 bit

Which drivers do I need & where can I get them ?

Do I need new BIOS ?

I am not a techy but

Dell says that Vista will not work on this machine which is strange.

Machine Specs are :

Intel Pentium D 3.0 GHz Dual core Processor

2.0 GB DDR RAM

250 GB HDD

256 MB ATI Radion X600 Video Card capable of running two monitors

Broadcom NetXtreme 57xx Gigabit Controller

Conexant D860 56K V.9x DFVc Modem

SoundMax Integrated Digital Audio

NEC DVD+RW ND-3530A

SONY DVD-ROM DDU1615

Please can someone give me a step by step as to how do I install the drivers too.

Thank You in Advance.

reason dell says wont work is there are no vist drives as far as i have searched try using a closer sister model that runs vista download drivers for that and see how it work the tricky bit will be the processor controler driver as well as the bios my need to be updated buy a process called flashing good luck man