This could be entirely normal depending on the environment (number of users, amount of traffic, etc).
However there are definitely issues that can create this problem as well. To start with I would ensure that you have a newer image on the wireless device. Haven't worked on the 880 ISR's myself, but I believe the AP runs a separate image then the router itself (someone with experience, please correct me if I am wrong). You should find details on the Cisco web site.
Second, I would make sure that the wireless drivers are upgraded on the client devices as older drivers can be a source of significant performance problems. In Windows, this is unfortunately not always a simple process. With some wireless manufacturers, there are updates through Windows update, some provide driver updates on their website and some you may need to get the drivers from the chipset manufacturers website.
From there, try to make sure you are on an uncongested channel. You will want to use channels 1, 6 or 11 (or 1, 7 and 13 if you are in a country that allows the use of channel 13). If you don't have the tools to measure channel utilization, you may have to experiment for the best channel (the AP should be able to provide you with channel utilization on it's current channel).
A simple tool, such as inSSIDer will give you an idea of how many other networks will be overlapping with your current channel, however this isn't a complete picture as it doesn't indicate if any of those networks are busy (i.e. causing high channel utilization). Being on a channel with a very busy network will generally be worse than being on a channel with multiple non-busy networks, but often this will get you headed in the right direction. Also keep in mind that even with the right tools, you are only getting a picture of "this moment" and "this specific location" view of things.
Beyond that, there are many things you can still do to improve performance, but I don't want to turn this into a novel. For instance, you can look at dropping lower data rates (1, 2, 5.5 to start), disabling 802.11b, turning off protection mechanisms (or turning them on depending on the situation), reducing the number of SSIDs (if you have more than one), using QoS, and many more wireless tweaks. Many of these are dependent on your environment and needs though, and there is nowhere near enough information in the question to know which may be best.