A proper way to put code before </head> tag

[OZO]

@JJoe - thank you!

I've tried the first two methods (I'll try the 3rd method later) and both works well:
1st puts custom CSS after other CSS declarations (right above </header> tag)
2nd puts custom CSS at the top of all other CSS declarations
That's exactly what I need to know

My question has arrived after I discovered that for the users of IE6 my "Google Light Theme" small filtering package (it's published here) becomes incompatible with the latest 2010-10-23 Sidki set. (I use IE7 all the time and just noticed that problem with IE6 and the new set). The new set caused Google to send search results page with a special format (different from other browsers). It happens when it gets "User-Agent MSIE 6.0" (the new filter set starts to send it with IE6, instead of old fake "Space Bison/0.02 [fu] (Win67; X; SK)"). And that format doesn't contain <noscript> tag (it was part of Match criteria that I used in filter). That's why I asked for help to find out the right way to put custom CSS code at the end of <header> part.

But, unfortunately, there is no happy end of the story so far. The specially formatted search results page is based on TABLE's, not on DIV's (as they send it for any other browsers and all versions of IE, except IE6). And this creates a big difficulty with getting rid of the left side bar and the empty right side bar

So, now it seems that the only solution to run those "Google Light Theme" filters with the new 2010-10-23 set and IE6 is to fake "User-Agent" string. And with Google's search results page - always sent fake "Mozilla/1.22 (compatible; MSIE 7.0; Windows NT 6.1)" (or containing anything else, except "MSIE 6.0"), which could be done with the help of "Exceptions.ptxt" file:

Code:

# Google Search - results pages
www.google.(*/)+{1}search\?
  $SET(0=a_ads.a_target.i_popup_b:0.i_timer:2.i_noscr:3.)
  $SET(0=f_ua_§Mozilla/1%2e22 (compatible; MSIE 7%2e0; Windows NT 6%2e1).)

(the added new 2nd line of $SET makes it happen)

But it means that all other browsers (including FF, Iron, etc) now start to get search results page with "User-Agent MSIE 7.0". It's not a big deal (as tests show), but it's not the right way to fix the problem, associated with only IE6, search results page and 2010-10-23 set...

I guess it could be avoided if there was a way to force to send a fake: (User-Agent MSIE 7.0) string only if:
1. the actual browser is IE6
AND
2. the page visited is "www.google.(*/)+{1}search\?"

But it seems that there is no such way to specify the "exception" in "Exceptions.ptxt" file. So user of IE6 should make change (see code above) in that file manually if he wants to use IE6 and (probably) to change it back, if he wants to use any other browser. Not a good thing...

Thus the question is - is there a way to send a fake User-Agent string only when user uses IE6 and he visits "www.google.(*/)+{1}search\?" ?