Dose the SMC unit have external antenas?
If so you can check into a better antenna.
We ran an SMC wireless AP here in an open air out door run of over 200 feet for about 2 years and the unit just last week finally died in a power surge.
That being said, at home I use Linksys Wirelsess cable DSL router with the fire wall built in and the 4 port 10/100 switch and it has worked very well with good range.
For a multi floor setup I recomend placing the wireless unit in the top floor near the floor in the center of the house, run your RJ45 eathernet cabel to the wireless AP unless a cable outlet is near then put your router there too. If you still get bad connections youll have to zone the house. probably up and downstiars or in vertical halves. The best solution is to use a newer product called a wireless repeater, it just needs to be plugged into wall power, it pickes up the main wireless AP signal, boost it and re transmitts it. You can also get a Zoom air wirless AP and they offer a complete line of antennas, I tink the indoor omnidirectional 12 Db antenna is like $80, we use the Zoom air units for out door wireless bridgeing up to 2 miles with their outdoor 13 Db directional antennas. 802.11b is the current standard with file transfers at about 11 mb/s, if your starting out from the ground up the new standard is 802.11 g and it offers 54 Mb/s rates and I know Linksys new G line is backwards compatible with ALL 802.11b DSSS systems.
There is NO need for a second router or modem, you just need to relocate or extend your WiFi.
On CDW a D-link repeater is $75, if the SMC router is a POS then I would recomend the Linksys Wireless AP/ router, its available in the new faster standard but Im not sure abot the repeater.