rebuilding website

now without frames

[colinf]

Hello,
i built an online travel agency in German for a client which was frames based (circa 700 pages).
It has been up for 3 years and has about 1500 other websites linking to it.
Now the client wants the site completely rebuilt but without frames. My question is, do i leave the old site on the server and redirect with a 301 (if so for how long)? Or do i delete the old site from the server and use a 404 explaining to the vistors what has happened. I do not want to get penalized for duplicate content if i have both site up at the same time.
thanks
colin

[outrun]

Ive done a similar thing, its not that difficult to keep the same page names is it? All I did was kept the same file names and change the index page not to have frames and added in navigation to the child pages, remove any script that forces the child pages to a frameset, if the pages where well linked there should not be a problem at all.

regards,
Mark