I am also a DWay user, yet I have a Commercial System (their best), and it has taken an act of war to MAKE them correct my speed problems.

Being on Sat-Mex 5, you are 'sharing' bandwidth with so very many other users that the speeds you are getting will only continue to go down and down.  I am assuming that you have done all the things that Tech Support suggest for 'tuning' your PC, and I assuming that you are absolutely pointing straight into the funnel on the Satellite.  (Despite what they say, it is worthwhile to "tweak" the dish alignment in small increments until you achieve the best possible signal.  I've had a tech out to my place six times, and finally we are getting a peak Signal Strength of 97 using a .98m dish and DW6000 Commercial modem.  Wiring to and from the satellite must be perfect, and preferably less than 125 feet (otherwise you should have an inline amplifier on one of the wires).

*If you are going to attempt realignment on your dish, please only do so if you are absolutely sure you are familiar with the proper procedures ...or you could easily "lose" your satellite (which can be just a tad frustrating)!

The LCCU "one setting for everyone" isn't always the best settings to use.  (For instance, I have Automatic Settings checked, and both of the lower boxes checked as well ...and it adds 200Kbps to my download speed every time)!  What I am saying is that in the IE browser I have both of my Proxy boxes checked ....and it is an improvement for my system. I'm using XP Pro SP2.  

I would check into PCPitstop.com and run the machine through the series of their tests to 'trick out' your settings ....every little bit helps!
www.pcpitstop.com   You can also do speed tests here, or at www.toast.net (for comparisons), yet this site (www.testmy.net) is MUCH more informative and accurate than any other I am aware of other than government run setups not available to the public.

You may be able to talk DirecWay into letting you "point" your dish to an alternative satellite to get your speed 'up there' too.  They can't turn you down if you press them hard enough (and have a clear shot to another one of their 'birds' up there.  (To get their attention, I stopped allowing them to charge payments on my charge card ...and THEN they started paying attention to my 'bitchin' (excuse me).  

I will try to keep up with your post, assuming I can find my way back here!

Cheers!

The Reverend