IP Address and DNS setup

Hello,

what I can do if I have not dedicated IP address but I share the address with more than 100 webhostings? If I use IP address to domain mapping, will this works? Should I setup DNS record like in the manual?

Second questions is, that I have possibility to setup domain www alias by writing the folder where to redirect the domain. If I redirect the domain which I want to map to my folder where is the WPMU installation - will this work?

Hope you understand,

R.K.