Look into getting a scanner that can quicly scan the slides, somthing that uses a USB, USB2, Firewire(ieee1394), or SCSI interface. I would steer away from the SCSI interface because you will have to buy a separate card for it. Firewire cards are getting pretty cheap, so that may be an option. USB will always be around, and it has decent speeds.
As far as scanners, will you be scanning the little 35mm slides or are they big negative type things like an x-ray? If it is the 35mm ones, buy a slide scanner. you will probably only be able to scan slides and 4x6 photographs on it, but they have decent resolution. Or look into a flatbed with VERY high resolution. Greater than 1200x1200 optical. Somthing like maybe a high end Epson or HP. I am sure that there are others, but I am not an expert.
Video cards - GO with a Matrox maybe with a dual head and a digital connection for a FP LCD monitor. That will make going to 2 monitors, or upgrading to a LCD much easier. and they have good 2d quality.
I hope that this gives you a good idea.
Paul