I have a client that is sitting on our wireless network, when ever they download anything from anywhere they just lose the data stream, as soon as they click resume then the data continues. They are the only one on the network that is having this problem. All the other clients in the area are fine. Their signal strength is -33 so I cant understand what is going on. There pppoe connection is fine so what could be the problem. They are using a senao 802.11b router.

I have a client that is sitting on our wireless network, when ever they download anything from anywhere they just lose the data stream, as soon as they click resume then the data continues. They are the only one on the network that is having this problem. All the other clients in the area are fine. Their signal strength is -33 so I cant understand what is going on. There pppoe connection is fine so what could be the problem. They are using a senao 802.11b router.

I'm not sure if i understand you correctly, but are you saying that the client looses connectivity whenever the load increases?
If so, sounds like a power problem to me (too low volt?).

This is a wierd problem, if he browses then its fine, but as soon as they download then the problems begin, but there is no pattern, it could be 500k file or a 23meg file. It happens after a few sec's but mostly after like 4 to 5 min. If you make a new request then data starts to flow again. I am running mains power to the router at the top so I doubt that Low voltage could be the problem. The connection is there its seems more like a timeout of some sort, but their pings are good. I have also tried both local and international sites and it gives me the same problem. Though it I copy something of the highsites ftp server its doesent time out at all.

This is a wierd problem, if he browses then its fine, but as soon as they download then the problems begin, but there is no pattern, it could be 500k file or a 23meg file. It happens after a few sec's but mostly after like 4 to 5 min. If you make a new request then data starts to flow again. I am running mains power to the router at the top so I doubt that Low voltage could be the problem. The connection is there its seems more like a timeout of some sort, but their pings are good. I have also tried both local and international sites and it gives me the same problem. Though it I copy something of the highsites ftp server its doesent time out at all.

It kinda sounds like a duplex mismatch on ethernet or mtu problem (sudden loss of large packets). I'm sure you've already checked that. How about replacing the radio card? Also sounds like a faulty card (stalls) or ethernet chip not acting properly if flow-control is enabled (disable this on customer equipment if possible).

Well the Mtu are set Now(sort of forgot about that one) the wlan card on the high site is fine cause they are the only client on that interface with the problem. The router at the client side has been replaced aswell and still no change. Mtu on interface is 1500 the ppoe server is set to 1480 and the firewall is set to 1440. They are connecting to the router via an switch that is in the office, so maybe that could also be the problem, but when they copy data from one another then it works fine.

This weekend i came across a case which is (in my opinion) identical to what you describe. It turned out to be the realtek card the user had. Perhaps a driver issue or more likely a chip revision.
See if replacing the nic(s) with a different card of a different brand (non Realtek based). I always recommend Intel NICs.
Some posts on the FreeBSD lists suggests that there is an undocumented (afaik) issue with certain realtek cards that do exactly the same as you describe.