Sadly, as of Maya 4.5, Maya ONLY supports shadow casting for hardware-rendered particle types of Point, MultiPoint, and Sphere. NOT Multistreak
Are you using 5.0? if so, I'll have to re-edit this post after I've had a chance to check my 5.0 docs at home in case this may have changed with the newer version.
Anyway, just an fyi:
By default, all particles are evenly lit, regardless of where you place lights in the scene. For some effects, you might want moving particles to drift in or out of the lighting, disappearing when not illuminated.
For example, you might want cigar smoke rising under a lamp to show only when it passes through the lighting. Or, you might want rain to show only when it passes beneath a street light or in front of the headlights of a car.
If you use Streak, Point, MultiStreak, and Multipoint render types, you can use lights to create these effects.
Sorry I couldn't be of more help regarding this, but I'm affraid you might have to render using a different render type
SOME EXTRA HRB TIPS pertaining to HW particle rendering:
**If you are rendering particles that have a Particle Render Type of MultiStreak or MultiPoint, and you want the particles to be softened or blurred, turn on Multi Pass Rendering and set the Render Passes value (the higher the value, the more blurred particles will appear).
**If you want particles to appear motion blurred, increase the Motion Blur value (the higher the value, the more blurred particles will appear), and set the Render Passes value to at least the Motion Blur value minus 1. (For example, if the Motion Blur value is 4, set the Render Passes value to at least 3.)
To render particles with Motion Blur, you must either turn on the particle's Cache Data attribute or select Solvers > Create Particle Disk Cache. Otherwise, the particle may behave erratically when rendered.
Israel "Izzy" Long
Motion and Title Design for Broadcast-Film-DS