The president signed into law an $8000 TAX CREDIT not down payment assistance. To qualify you must meet Income Guidelines and be a "First Time Home Buyer" (i.e. not have owned a house within the last 3 years).You buy the house and when file you income taxes you can get the Tax Credit which will come to you in the form of a refund.
In the modern computerized age we're in today we often forget that comps derived simply by address do not consider all the attributes of a property when spitting out a number. I have found that often when Foreclosures are factored in, while a legitimate sale, you cannot truly compare a distressed property with a property that is updated and move in ready. To truly get a fair market price comparison, I believe the property must be seen. Often the "street view" can be deceptive, both positively&negatively. Have a local real estate professional do a Comparitive Market Analysis for you or pay for a professional appraisal. Either way will give you a true fair market value for your townhouse.
Under the most recent and current Stimulus Plan, the $8000 does not have to be repaid if you own the home for at least 36 months. The previous $7500 credit was an interest free loan from the govt. that required repayment of $500 per year over a 15 year period.
You certainly need someone to look out for your interest. An agent can give you a fair estimate of closing cost as well as review the sales contract, and determine the current market value of the condo you are interested in buying. Sometimes having a pro to look over things can save you lots of money and headaches.
If your fiance has not owned a home within the last three years, they may still qualify as a "first time buyer". The other side to the question is will both incomes be used in qualifying for a mortgage? If only yours is to be used, buy the home yourself, not jointly and you will qualify for the $8K tax credit.
The answer really depends on your motivation to sell. Do you have a financial burden in keeping the home now? Are you transferring and need to move? Has your personal situation changed so that a move is necessary? Have you found the "home of your dreams" at a fantastic price? If the answer is yes to any of the above, then selling now might be the correct answer. You will need to consult with a local Realtor to get a Current Market Analysis for you property to really establish the value of your home.