I have been working with the same problem for some time now and I've developed a couple of solid work flows for setting pfx hair that doesn't go through your geometry when moving...
My most recent setup is using a cloth mesh to deform the pfx hair- this can be done by setting a piece of cloth laying over your characters head and draped down the back the length the hair will be- you then make whatever surface will come in contact with the cloth or your pfx hair make a collision object with the cloth geometry- then you select the cloth vertecies that are on top of the head and then shift select the head and under cloth menus
CONSTARIN>MESH CONSTRAINT - this will ock those verticies inplace on that surface- Now draw the pfx hair on the head gometry while hiding the cloth Now create controle curves for the pfx hair- how ever much of the hair you want to move independently of eachother should define how many controle curves to use I DONT recomend using more than 3 to 5... Now select the pfx curve and next the controle curve you've designated to set up to drive the pfx curves or curves you previously selected and in the Render Menus select under Paint Effect>Curve Utilities>Controle Curve... Now you have a controle curve that the pfx curve will follow now after setting up all the controle curves . Select all the controle curves shift select the cloth go to under Animate Menus DEFORM>CREATE WRAP, this create a wrap deformer for the control curves to the cloth object almost by way of being constrained in a sence by a lattice... Now as long as your collion offset, collision depth, & coliision priorities are set up corectly the cloth will bounce or fall over surface without penetrating them and because the controle curves are fixed to the cloth they cant penetrate the surfaces thus because your pfx tubes/ curves are constrained to the control curves they cant' pass throught the surface- you will need to adjust the offset values for the controle curves under the attributes for the pfx curves under the forces section to get it perfect but this seems to be working great- I'vfound with the right setup you can even have situations like your character brushing there hand through the hair without penetration... If you don't know cloth that well or not enough to complete the operation you can you the controle curves like you would set up for the pfx hair on the head in the last without setting up the cloth, the only difference is first you draw the pfx on the head then in a side view starting at the base of the head at the back of the neck-draw yourcontrole curves starting there going the length to the end of your hair(try keeping the control curves 1/2 way between the characters surfaces and the pfx hair) Now take the curves and in the soft bodies menu Duplicate creating soft keeping original as the goal- Now Parent the original made controle curves to the head so they wont mpve from that position now select the pfx hair and the corresponding soft bodie curve to become thecontrol curve like in the above- now you can set up collisions on the soft bodie curves sothat they can't pass through the characters geometry you'll have to make adjustments in the forces attributes of the pfx curves like above -suggets trying to make the hair lie almost on the soft bodie curve- also suggest when duplicateing the curves to soft original make the goal eight one to start then in the component edidtor adjust the weights as needed suggest on the 1st partical cv be a stiffer value then less al the way down-say your controle curves have 7 cv's then that means you have 7 soft particle cv's with weights to those 7 reg cv'ssuggest wieghting down from top cv like
cv1= 8, cv2=6.5, cv3=5, cv4=4, cv5=2.5, cv6=1.25, cv7=0... adjust as needed for movement -only prob with ths method is its not quite as reliable, penetration occures on occasion, work arounds key frame offset values for control curve in the pfx hair forces atrribute to attract or move away from the soft bodie curve at those frames- you can also bake the dynamics on the soft bodie curves and push points around at the end to correct it- make sure if you bake you disable all collision and forces effecting the soft bodie curve -canbe done in the Dynamic relations editor...
-Personaly I find the Cloth way Best but the soft body curve works well to - curently putting together tutorials on both methods along with creating a cloth rope to post on the web, check listings for post-probably within the next month...
Good Luck
sid69 sid69graphic@yahoo.com
student @ Ex'pression Center for New Media, Emeryville CA xnewmedia.com