1. A rental agreement in Austria is for a minimum of three years, if your apartment is under the jurisdiction of the 'Mietrechtsgesetz' (MRG - Austrian tenancy law). Yes, three years. So think twice if you're coming here for a good time, not a long time.
If so, perhaps search for a room in an established flat - newspapers Der Standard and Kurier have listings online, as do www.jobwohnen.at and www.airbnb.com.
In Austria, it is perfectly legal for a tenant to sublet their room, as long as the number of occupants in the apartment does not exceed that stated in the contract. (Your landlord may not like it, but the law overrides them. Prosit.)
The three-year rental contract is mainly to safeguard the tenant, not to protect the interests of the landlord. For example, landlords cannot put the rent up whenever they choose (instead it increases every 12 months, indexed to inflation) and after one year a tenant may leave at any time, giving three months' notice.
2. Apartments are almost always rented empty in Austria; you must fill it with your own stuff. By law, an apartment must include functioning central heating, hot water, a kitchen sink, stove top and a shower/toilet, unless you've chosen to live in an extremely old, rundown 'category C' apartment, with shared bathroom facilities. In which case you are getting it SUPER cheap, so stop your whinging and find a friend with a Jacuzzi. Rubber ducky, you're the one...
3. Most landlords will require you to take out Contents Insurance. This is available as a standard product from insurance companies and your premium will depend on the size of your apartment and the number of Rembrandts, Chagalls and bottles of 1951 Penfolds Grange Hermitage you have tucked away.
4. In Austria, your rental bond/deposit (Kaution) is usually 3 months' rent (and can be up to 6 months' rent if the apartment is super swish, furnished, etc). Ouch. Quite a hefty chunk. However if you're under the Mietrechtsgesetz, you are then sitting on some pretty tight tenant protection laws, so all in all, worth the initial financial pain.
5. Your estate agent may do next to nothing for their fee. They will show you a property, but the moment you indicate your intention to rent it, they will disappear in a cloud of smoke, invoicing you for one months' rent along the way (and up to two months' rent if your contract is for longer than three years). Cushiest job in the universe. If there are initial repairs required, don't bother talking to the agent, discuss it directly with the landlord before you sign the contract.
6. If your agreement comes under the jurisdiction of the Austrian Tenancy Law (you should really check this) it takes precedence over any rental contract. It includes rules that regulate the maximum rent that can be charged on a property and limit the length of tenancy agreements. So no matter what crazy stipulations your landlord may have slipped into your contract before you signed, if it is outside the law, it does not stand. Pretty good, huh. Break out the Penfolds.