Problems with Safari, tabs, radio buttons, etc.

Question

My goal is (as you probably guessed) to have a script that unite all open windows/tabs in the frontmost window. I know at least of two theoretical ways to do this, but neither works for reasons I don't understand:
1. GUI scripting. Use Safari's menus to navigate through tabs. For some reason this works somewhat randomly, sometimes getting all tabs and sometimes one tab per window. I can get it working in an awkward way that removes all windows before opening a new one: not exactly what I want to do.
2. I have found this one browsing for solutions on the web, and it uses the System Events app. It seems that Safari tabs are "radio buttons". However, the number of radio buttons returned is always 0. Also, reading the URL with the line
value of text field 1 of group 1 of splitter group 1 of window 1
does not work (returns NSReceiverEvaluationScriptError: 4).
So, does anyone have any ideas on what goes wrong? (or even better, does anyone have a script that works?)
Mac mini Core Duo   Mac OS X (10.4.7)  

Answer 1

Thanks Cyclosaurus, this seems to work!
There is still one problem: when getting the URL of a window, if it is empty it will throw an "undefined variable" error. How can I avoid this? (I cannot even check if the url is empty because it is undefined.)
Here is the script I have so far, if anyone is interested:
tell application "System Events"
tell process "Safari"
try
-- finding the group
set tab_group to 0
repeat with g from 1 to count of groups of window 1
if buttons of group g of window 1 is not {} and title of button 1 of group g of window 1 is not "" then
set tab_group to g
exit repeat
end if
end repeat
set URL_list to {}
set N to count of windows
repeat with w from N to 2 by -1 -- going through windows
set T to count of buttons of group tab_group of window w
repeat with b from 1 to count of buttons of group tab_group of window w -- going through tabs
click button b of group tab_group of window w
tell application "Safari" to set this_URL to URL of document w
if URL_list does not contain this_URL then copy this_URL to end of URL_list
end repeat
tell application "Safari" to close window w
end repeat
set C to count of URL_list
repeat with i from 1 to C
my new_tab()
tell application "Safari" to set URL of document 1 to item i of URL_list
end repeat
on error the error_message number the error_number
display dialog the error_message buttons {"OK"} default button 1
end try
end tell
end tell
on new_tab()
tell application "Safari" to activate
tell application "System Events"
tell process "Safari"
click menu item "New Tab" of menu "File" of menu bar 1
end tell
end tell
end new_tab
Mac mini Core Duo   Mac OS X (10.4.8)