Hi Cooper :thumbsup
Firstly you need to check what bulb type your car is, there's a bit of confusion when you check Halfords etc - it will either be H1 or H7. Get your bonnet open, unclick the headlight cover on one side and have a look at the bulb.
Now I have an '99 E36 and I have H1, but yours might be different.
H1 bulbs look like this;
This one is H7
Now, I don't think you will receive any error codes or any problems as it seems to be the E46's and newer that have these problems so you should be fine :thumbsup
However if you have an 18-button OBC I might need to ask someone to double-check on that.
Now you mentioned getting a 55w HID kit. I would consider getting a 35w HID kit instead.
The most popular and easy to buy is 35w, this is what I have have and what most people on here also have that have converted to HIDs. I have seen someone in my village with a 55w HID kit and they were so bright they were painful - I would recommend staying away from this as you're likely to blind oncoming drivers as well as draw more attention from the Police etc.
6000k is in my opinion the best colour temp to go for - I have these are they really look the business. They give a pure white light with a slight bluey tinge. Any lower than 6000k and you'll have white-looking lights but a tinge of yellow. Any higher than 6000k, such as 8000k and you'll have noticeably bluey headlights - these give out less light and are more likely to attract trouble from the police, since you are only allowed white or yellow headlights.
Bi-Xenons - You could convert your high-beams to HID as well, but I don't think it really necessary and can be a bit more tricky to install - installation is plug and play with the wiring, however you have to mount one ballast for each bulb, and if you were converting to Bi-Xenon then you'd possibly struggle to find space for all 4 ballasts.
Also, HIDs take a few seconds to warm up, and if you have the need to flash oncoming traffic they don't work so well. This is because when you turn HIDs on they flash very bright for a split second, then dim right down before taking a few more seconds to light and warm up fully.
I got my kit off eBay last year and my kit is still going strong (touch wood). If you want piece of mind then you could purchase a kit from
Hids4u which are around £100 mark but have a warranty as they are a proper retailer.
I have written a How-To guide in the link below which should help give you an idea on installation etc. Hope this has helped, best of luck and let us know how you get on
http://www.bimmerforums.co.uk/forum/f3/hid-xenon-conversion-e36-diy-how-to-t10732/