With the assumption you know about trunking, digital, and rebanding:
1) You'll need conventional analog scanning for UW, Capitol, State, Dane Co, airport, and Municipalities, in general.
2) You'll need analog trunking for most City of Madison services.
3) The only digital services I know right now are Truax security, fire, and ops. Unless you're in the viscinity of the airport, may not be an issue.
4) You'll need to consider future digital trunking requirements for Dane Co and the State. That may be a while (due to RFPs and budgets, etc.), so unless you're not sticking around in Madison, the point may be moot. However, depending on where you move after school--so MANY places are going digital it may be a good investment now. If you do any travelling, or plan on keeping this for a while, get digital.
5) Costs: A good analog handheld, i.e., Uniden 246 or 300 is about $225. A good digital handheld, i.e., Uniden 396 is about $525. You can find used ones at reduced prices that'll do the job at a few dollars less. Watch out for some of the sales, i.e., Radio Shack Pro-97 would be a great analog trunking scanner for now--still on sale for $150 at many stores, but it'll not be friendly, according to reports, when rebanding is required (which may also be a while in this area--schedule is uncertain). These are handhelds--you may also wish desktops/mobiles (but handhelds seem to be more popular if you're mobile a lot). Search the forums and you'll find more discussion on places to buy and prices.
6) Rebanding is going to make some scanners obsolete. Read the articles below. Avoid spending $$ on a scanner that can't handle rebanding.
The following may help clarify more (also use the Wiki to search for more info):
Rebanding (inititially scheduled to be done by 2008, now just started):
http://www.wpascanner.com/wiki/index.php?title=800Reband
and
http://www.grove-ent.com/radiorumors.html
Programming/Trunking:
http://www.grove-ent.com/SCANNERPROGRAMMING.htm
Frequencies you indicated of interest:
Dane Co:
http://www.radioreference.com/modules.php?name=RR&ctid=3064
Madison:
http://www.radioreference.com/modules.php?name=RR&sid=1451
Statewide:
http://www.radioreference.com/modules.php?name=RR&stid=55
Where to Buy (check around, but get from a big dealer with good service), some examples (no preferences impled)--again, search the forums for other opinions:
http://www.grove-ent.com/unidenscanners.html
http://www.universal-radio.com/catalog/scanners/1396.html
http://www.scannerworld.com/content/product/model/BCD396T
http://www.scannermaster.com/
http://www.123radios.com/BuyItNow.asp?PID=509
You will want to consider using computer software to program the scanners--it's much more enjoyable than programming via the keypad. Uniden scanners come with software--free on the digital ones--that's quite acceptable. Many prefer low-cost commercial pieces of software from Butel for either Uniden or Radio Shack scanners (have some enhancements):
http://www.butel.nl/ Other popular Radio Shack programming packages:
http://www.starrsoft.com/
That should be enough to chew on for starters. Hope it's a brief but to the point discussion. My bottom line recommendation? Go digital with something like the Uniden 396 (but feel the $ pain) if you're in it for the long run, or go for something like the Pro-97 if you're in it for only the short run (but know it'll be obsolete soon).