New install on but want to build it first before going live

Hi

Not strictly a support question but hoping to pick up some help from you or the community please.

I am not new to building sites but I am new to WPMU and I am loving it, so much so that I want to take an existing site created with a xsitepro and change it to a wpmu.

Question is whats the best way to do this as I want to keep the old site running while I populate the new one so I cant install on the current root folder as this will cause conflicts I guess. Is there a way to build the whole thing on a dummy domain and then move it when tested?

Any advice please.

Also any tips on a quick way if there is to move html pages into wordpress would be great.

Thanks in advance

Gary