Your husband's side effects sound pretty normal. First, I would get Ben Williams' book "Surviving Terminal Cancer". Or download his latest GBM Treatment summary at: http://www.virtualtrials.org/williams.cfm
. It will inspire and inform you.
The Dilantin, the tumor, and the radiation all work to make you drowsy and dizzy. With careful help from a doctor, he could try switching anti-seizure meds. Or he could try lowering the dose. Or, he could try going off of them altogether (with the consult of your doc!).
Try some other things to help boost his energy, including red blood cell boosters (talk to your oncologist) and supplements. Don't be afraid to treat the depression...attitude is an important part of beating cancer. You could even look into treating the depression with Chlorimipramine, which just so happens to also kill glioma cells pretty well(http://www.ncbi.nlm.nih.gov/entrez/quer ... t=Abstract
I would consult a more agressive, top-notch neuro surgeon to look at the prospects of resection surgery.
Also, your husband may simply need to rest for a few weeks. Good luck with it all!