My 2nd attempt! I made a spelling error in my first.
After having some problems accessing shares across the platforms, I've found that Acronis products as well as others can be at the root. The cure seems to be something about increasing the IRPStackSize. I've True Image 9 on one (XP) and 10 on another (Win7) and receiving errors accessing XP shares from the Win7 machine until stumbling into this fix. A google search will quickly find the regedit way to correct for this. For me the size needed to be at least decimal 21. Hope that helps someone out there.