Could be made far harder by using digital signatures and using Webstart to deploy the client. But we know that cheating is merely a manifestation of flaws in client/server game design, i.e players will always take advantage of every method at their disposal.
I was writing a MMOG once upon a time… my intention was always to open source the client code and make it available for free.
Cas 
depends how u go about the game u are making. you can get around cheating in simpler ways. if a player had 20 skill point, then the next day had 2000000 skill points- your software can prob guess they pull a blag somplace. also u can put timers on skilling or have the server when transfering assets around your game- track the asset… if u have to farm then the contents of the plot of land is managed by other game assets. so u cant magicly make an asset apear player side.
theres loads of ways to slow cheating. all very simple as part of the games design- when in comes to protecting data messaging from the server to the client- well thats always going to be hacked. all u can do there is hope you where not to blatent and be a bad speller like me
i wouldnt worry- ied worry more if yer explotion effects look cool and they all draw in the correct place :). sod cheating- people will find a way. and if u do patchs u can aways update the handshake code. or even send an update to the code when the player is playing the game (java rocks).