New internal HD

I need a new internal hard drive installed pretty soon and I have never done it before. I would appreciate any suggestions or warnings anyone can offer. I have an external HD right now, but I would probably keep the old internal as an external (enclosure). One concern I have is that my Tiger disk keeps spitting out when I need to use it for any reason. It will not stay in the drive at all anymore (shortly after the initial installation). When I install Tiger on new internal HD, would the Tiger disk give me trouble? I would not know what to do if Tiger does not work. I don't have any warranty left on it. Any thoughts?

Please see my new post about my experience installing a 2nd HD. I hope it helps some of us.

I took care of the problem of Tiger DVD spitting out. First, I put the DVD in the drive to install as usual. The DVD came back out as usual. This time, I pushed the tray back in again and kept the tray from pushing out. This worked only once for me, because I tried it only once. If I have further problem I will post.