Network Design for 600mts Away from Server.

UTP cat5 cable is garanted to work for distances of 100 metres maxim.

Depending on the trafic thru the LAN i would recomand you to use STP cable with at least one repetear about half the way. If the full 100mbs are used constantly you shpuld add more repetears.

How is the cable routed beetween biuldings? underground or aerial? If it's aerial STP isn't a very good choice because it will be afected by ground loop, UTP is much better in this case ;)

GooD LucK!

If you are trying to connect seperate building at that distance you may want to think about another media such as fiber or wireless. Depending if there is any type of interference you can get away with wireless but if you have a alot of heavy machinery I would go with the fiber because you will not have to worry about interference and you can go several kilometers

Go to fiber. You will be happier and keep your sanity.
Lee

My advice would be to bite the bullet and use fibre for any runs greater than 90M.

Use Cat 5 UTP only to wiring closets in the area close to requirements (max. 90M runs - this allows for patching).

Then use 50/125u multi-mode fibre to link between each wiring closet and your server room.

This will allow you to use fairly simple 10/100 UTP switches, within spec, for all PCs, printers etc. and 1000Base-SX gigabit inter-switch connections.

Note; don't use standard 62.5/125u mmf - it only supports up to 220m, as opposed to 550m for 50u.

You can use repeaters every 100 m, but I doubt that this will be a convenient solution. UTP is rated for 100 m - period. It can be stretched farther under ideal conditions, as you've already discovered, but you put your network equipment at risk doing so. The reason for this is that UTP cable looks, primarily, like a distributed capacitor to the circuit driving it. The longer it is, the more instantaneous current the driver circuit has to feed it to achieve the desired logic levels at the far end. By extending the cable so far you are hanging a huge current load on your source equipment, and will thereby shorten the life of the hardware. That it will become unreliable under non-ideal conditions you already know...

Fiber is a good solution, as others have suggested. It's expensive, and requires that you pull some cables that you might not have the ability to do. If the existing UTP cable has some wiggle room in the conduit, you can probably get away with it - just use the old cable to pull the new fiber through the pipe and add optical to electronic adapters at each end.

Another alternative, though an expensive one, is to convert the WAN links to wireless. Residential-grade 802.11b cards and access points are rated for 100 m, but mine works fine at a range of 4 miles or so because of a high gain (18dBi) antenna I installed. You'll need a clear line-of-sight between the antennas, but you'll save yourself the hassle of pulling cable.

You have to "go up" to a new technology .
Choice 1 : Fiber ( best speed GBit ! most secure , more expensive than wireless )Buy a total of 4 modules ( 1000BaseSX) for your 3Com switches if you bought models with slots. If not , either buy new models with the modules . Or a cheaper solution is put media converters at the and of the links .The speeds depend on your available UTP ports . Can be 100FX or 1000BaseSX ( be careful with your fiber termination and port adaptors/connectors they should match ..all must be SC ). You would need 4 suitable fiber duplex patch cords.
Choice 2 : Use 2.4Ghz wireless 802.b/g , the latest ones go up to 108MB. I suggest you go for cisco 1310 . For many reasons . Do not want to enable WEP , plus EAP for security . You need to buy 3 . One at the center , 2 at the other buildings . The antenaa are integrated and you dont need more than that for this distance.