Ideas for prefilter for a msr miniworks?

Don't know the specifics of why you want to go through the hassle of a multi-step pre-filter system just so that you can use a 1 lb. filter that IMHO (having owned one – and then promptly got rid of it due to it clogging so frequently) is a pain to use. I like both my Steripen Adventurer Opti with a .1 micro BioDiesel prefilter, and I like my Sawyer PointOne Squeeze filter (with AM in case of hikes in possible viral infected areas). Just my 0.02 cents worth. I'd ditch that idea of getting the Miniworks and look for something lighter and faster / easier to use. Both the Sawyer and the Steripen are right around 3.5 oz. – even bringing both would be less than half the weight of the Miniworks.

You could use just about any brand of prefilter. MSR makes the 25 micron "Siltstopper" if you want to add more weight and cost– about $20 at REI. You can buy the MSR Sweetwater prefilter that is basically a screen that stops the big chunks (75 micron).

MYOG gear options usually lean to using a bandanna, coffee filters and so on. I made a coffee filter holder from a Seal-A-Meal bag that will sit in the top of a pot or wide mouth bottle. You can make coffee with it too if you are careful and patient. See http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=44546

Using your cook pot is the best method I have seen for water transfer. If you are freaky about contaminating the pot, a quick flame session should do the trick. With a Steripen, I used a simple smooth-sided drinking water container like a Smart Water bottle with the top cut off so I could fill it with other gear to save space. In a perfect world it could fit around your filter or pot. I've used cut down milk jugs as sinks and a 1/2 gallon plastic jug with the top cut off would make a good water transfer container.

+1 on the Sawyer Squeeze filter and carrying backup chemicals with any filter system. Stuff happens.

Im not familiar with the Miniworks filter, but I use two layers of pantyhose stretched over a Nalgene to keep silt out before using my Steripen. Seems to keep particles out pretty well for my use.