Meanwhile I managed to find a good page describing how to set up a Pi like i wanted.
Thanks for the comment.
I've made a few changes to the page based on the comments you included.
1/ Not for beginners?
When I created that page it was based on discussions on the forum I was having with people that were already quite familiar with Linux, rather than aiming at people that are new to Linux. I therefore made a few assumptions about the person that was reading. The more I follow the forums it seams that other people have a network connection, but no TV and so sounds like others may be having this problem.
I still think that most people looking to get started with the Raspberry Pi really should be looking to connect it to some kind of TV or monitor before going headless, but I've added a couple of things to make it a little easier (spelling out the dhcp search process and providing the link to Wheezy).
2/ Regarding the link to the Wheezy Debian image.
I didn't link to the Wheezy image partly because of 1 above, (those I were discussing this with were already using Wheezy) but also because I didn't want to make the document date too quickly.
Many of the other tutorials on my site have been around for many years, some of which were even converted from other UNIX ebooks (AIX / Solaris) I wrote before becoming more involved in Linux, and in that time they have needed very few updates (I've recently just gone through updating them which was more format conversion than changes to the commands etc.). Tutorials which are very specific about the distribution end up in my blog rather than the tutorials.
Whilst the Raspberry Pi is still in it's early stages it looks like I may have to update them fairly regularly anyway - so I've now added the link to the Beta download blog post.
I'm also hoping the Wheezy image becomes the default fairly soon, because ssh enabled by default and the raspi-config tool are going to make it much easier for new users.
Fixing Wireless problems headless
Regarding your current problem it's going to be very difficult to diagnose a network problem without some kind of monitor. Not impossible but I wouldn't recommend it. Obviously checking your physical connections / ethernet cable etc should be the first thing to try - is it a straight cable rather than a x-over? Have you tested the cable on another computer? How about that particular port on the router?. You can also try looking on the router to see if it is giving out a DHCP lease, which varies depending upon the router you are using.
Failing that you really do need to get down to hand editing the OS files using a separate Linux computer. But I would only recommend this for someone that has a reasonable amount of experience with Linux already as it's pretty messy.
If you mount the SD card then you can included commands to run at startup by using the /etc/rc.local file. This can be used to issue commands and save the output onto the SD card which you can then read by reading the SD card on a linux computer.
eg. you could log the output of the ifconfig file (which shows the status of the interfaces and whether they have an ipaddress) by adding
ifconfig > /home/pi/ifconfig_out.txt
You can also view any of the log files that are created when the SD card is in another linux computer (eg. look at syslog / messages / dmesg)
But I'd really recommend connecting to a TV / monitor and taking a look by running the commands directly rather than trying to diagnose a network problem without connecting to a screen.