Went to Borneo with Stuart over this Xmas and it was good. Although I can only talk about how it was during December.
Equipment is best to get whilst you are in the UK - camping shops are few and far between, not to mention larger sizes (I'm 6' 2"). The notable exception to this is things like billy cans, which are available just about everywhere, and often come in different sizes and varieties which may not be present in the UK. Given exchange rate fluctuations recently, you should find all the Zebra stuff pretty cheap too.
Food is of good quality and price, although if you like lightweight ratpacks, then bring those along.
Language is rarely an issue, especially in Brunei, although is a significant barrier when you get away from the major towns/cities.
We were advised not to wear any "Camo" gear, and I would have to agree. Stumbling across a boarder patrol in the middle of the jungle, they were intially very surprised to see us, and mistook us for army anyway - that's without camo.
Take lots of jungle moisteriser (DEET), and try to make sure people know where you are going and when you will be back. On the deet side of thiings, I would mention that some of our group took along 100% Deet, which was great for about 5 minutes, however, given the amount of sweating we did, it's better to bring some "sweat-proof" stuff, which may be a lower percentage. I would recommend the US army stuff (Ultrathon), which is cheap to get on eBay if necessary. It's better to have 33% on you, than 100% on the floor.
Enjoy - PM me if you need extra details!
Ag