Just the first CD would be enough to setup a basic install. If you have fast broadband connection to the internet (or a modem link but you don't pay the phone bill!), you can use the apt program to add everything you want.
However as you seem to be migrating from Mandrake, you might be in for a shock. Woody install is not nice to look at
If you want Debian and not the STABLE version which i s Woody, please try the live CDs which are really useful in many ways.
Knoppix
Morphix
and probably the best one of them all?
Mepis Linux at
www.mepis.org This has a GUI install from KDE and has a GUI partition manager too - in case you want to have two distros on the same PC. It has a nice supplemental CD too...
Have fun. Will travel!