As has been pointed out, there's no way to force normal links to open in the same window. This is the default behavior of our forum software, vBulletin.
To link to specific sections of a post, use the
[anchor] and
[jumpto] tags.
For example, if you want to be able to link directly to a section of a post, wrap some text on the page, like the section's title, in [anchor] tags, like this:
[anchor=races_section]Races[/anchor]
You can then create a link that "jumps to" that section using the following code:
[jumpto=races_section]Jump to Races Section[/jumpto]
It's even easier if you want to "jump to" an entire post on the page, because you don't have to create the anchor tags. To do this, right click on the post's number. It should give you a link that looks something like this:
http://www.gtplanet.net/forum/showthread.php?p=6595563#post6595563
Take that last section, 'post6595563', and use it in "jump to" tags, like this:
[jumpto=post6595563]Jump to Third Reply[/jumpto]
Here's what that link would look like in action; it should take you to the [jumpto=post6595563]third reply in this thread[/jumpto]. Use these links with caution, as they will only work if the anchor/post that you're linking to appears on the same page as the link (remember, other users might be using a different post-per-page setting).