Quick question - reinstalling OSX

[charpi]

So, here's the situation. I've been messing around with my iMac and stuff, trying to mod it here and there in terms of kernel and software and stuff ( I shouldn't have, I'm still new to this). Serves me right but now I can't boot it up, saying that it can't find some kernel files or something. Here's the thing, I inserted the iMac OS disc and it reads fine. So now I'm at the part where you select the hard drive to install OSX in.

Here's my question.

1. Will all my data be gone?
2. Will it replace all the erroneous files with the right ones so it can boot it up like normal again? (If I have 100GB free space, probably I'll have around the same amount left since little files were added and most were simply replaced)
3. Or will it add on copies of the OSX files, meaning that I have 2 copies of OSX on the same drive. (If I have 100GB free space before, now it's left with 90GB because of the installation).

Thanks guys.

 

[Hellhammer]

1. No, unless you do clean install

2. Archive and install will only replace the system files

3. No

 

[Gregg2]

Is this Snow Leopard? I still have Leopard, but I've read that SL doesn't have the archive and install option.

 

[Hellhammer]

Is this Snow Leopard? I still have Leopard, but I've read that SL doesn't have the archive and install option.

It does, just insert the disk and click install. For clean install, you have to wipe the HD with Disk Utility first so archive and install is the default option