While frequency weights do not allow for non-integer weights, the other types of weights available in STATA do allow non-integer weights. Depending on the STATA command, you have available as many as four different types of weights: fweights, pweights, aweights, and iweights. In general, it is preferable to use probability weights (pweights) for IPUMS samples.
Also, if you are interested in only one city, you can use the “Select Cases” option in the Data Extraction System to create a data extract that consists of only respondents from your city of interest. This will reduce the size of your data files. See here for more information on this option.
Hope this helps.