I have a MacBook, Tiger 10.4.11, memory; 1GB 667 MHz DDR2 SDRAM, processor 2 GHz Intel Core Duo.

My trash has refused to successfully empty for the last 4 months so I ran Disk Utility to try and fix what problem it might be. Every time I run Disk Utility to verify disk it gives me this;
Verifying volume “Macintosh HD”
Checking HFS Plus volume.
Checking Extents Overflow file.
Checking Catalog file.
Invalid sibling link
The volume Macintosh HD needs to be repaired.

Error: The underlying task reported failure on exit

1 HFS volume checked
Volume needs repair

I have run the install disk holding down C and it still can't repair. If I remember right it says something about B-Tree
What can I do to fix my computer?