I am using a cable/DSN router. I can connect remote pc's to about 30' away but not 150' away. What gives? Does the router sap signal strength?

The maximum length that a single CAT-5 cable can go is 100 metres (about 328 feet) and you seem to be easily within that. If possible, can you try connecting the closer machines together using the longer length of cable, just to prove that it’s not something as simple as a failed piece of cable?

Probably the cable and the router are OK. I suppose you are making
the cables yourself. With short lengths you don't need to connect the
wires in any special order, because the signal get fine if all the wires
are paralell. With long cables you can use the following standard scheme:

1 white/orange
2 orange
3 white/green
4 blue
5 white/blue
6 green
7 white/brown
8 brown

1 2 3 4 5 6 7 8
| | | | | | | |
___________
||||||||

Suppose that thing above is the connector, and the flange is back. Really it does not matter
what colours you use, the important thing is that you use a twisted pair for 1 and 2
wires (transmit), and another twisted pair for 3 and 6 wires (receive), because RJ45
only use this four wires. If you don't use the twisted pairs the signal will lose.
Good luck (and excuse my bad english)

Jack, the wires have to be in their correct order regardless of the length of cable - if not they will not talk to the NIC correctly.

The first answer is mostly correct - Ethernet is only good for total cable lengths from switch to PC is 100 metres. The reason for this is the signal strength reduces/changes over the length - any more than 100 metreand voltage pattern will change and the message will be either misunderstood or unreadable.

If you purchase a repeater or "active hub" this will regenerate the signal and allow for a further 100 metres.

Sorry jack, yes the wire on short cable lenghts can be in any order - as long as they are the same order on both ends of the cable

I'm probably repeating stuff from above but never mind. The only thing I can think of is interference. Just make sure that yor cables are away from lights and other interference generating doodads, and that if you really must cross over any other electrical wires you do it at 90degrees straight across them.