Adding wireless key bd & mouse

I have Dell hardware, Win XP 2sp soft and am trying to add MS Wireless
Desktop 6000 (Keyboard and laser mouse) I put in disc, hit start, run get
message -"conflicting software device already installed"
Well of course there is. Instructs say to inst using current board and
mouse (dell board - original- and Logitech optical mouse). When I ok to
remove I get "Install sheild engine (Kernel ex.) could not be launched. No
such interface supported"
Please help. I am 2 year user of this system but have never had trouble
installing anything before.