That's so close you might as well round up. Ghz really isn't the best evaluation tool for measuring CPU performance. It would be better to know exactly what CPU it was, AND, perhaps even more importantly, what video card you have. These days if someone asks if a game will run I am more inclined to ask what video card they have than what CPU, and at this point the only thing we know is you have a 2.7Ghz (probably dual-core) CPU. So maybe post a little more info on your rig.

i don't suppose there is a demo floating around?

is your card a Geforce 240?

Your CPU is hovering near the entry level for the game(and for CPU's out there in general), but will probably be passable. Athlon x2's are good if all you need is a good general use system, but they are getting a bit old, and don't make the best gaming CPU's.

The Geforce 240 was what came up when I searched the specs you gave. Assuming that is the card, it is listed as above spec for the game, but listed by a third party as the entry level card you would want to use if were playing the game. Bottom line is I think you could run it, but it probably won't be the smoothest gaming experience you have ever had, but may be good enough.

Given your CPU I would personally recommend a Video card upgrade to help offset any CPU deficiencies you may have. Provided your rig will allow you to drop in a new card of your choice (is it store bought?) and you can afford it. Tom's hardware keeps a list of best cards for the money and right now they recommend a Radeon 6670 for around 60$ which roughly about 50% faster than what you have, and a Radeon 7750 for about 100$ which is about double. I also like the looks of the Geforce 550 Ti which is about 120$, and would also use the Nvidia Driver set. (most cards can also be had for cheaper via rebates)

Passmark software has collected and published running CPU and Video card benchmarking results for just about anything you might have or want to buy. A searchable GPU list can be found here
http://www.videocardbenchmark.net/gpu_list.php

man you nailed it, thats exactly the card i have. good advice too, but i think what i'll do first is upgrade my cpu to a quad core, assuming my mother board can handle it. i might have to just scrap the whole system and upgrade to a brand new one, but if i do that it'll be next christmas at the earliest.

i might just buy dishonored for the ps3, all things considered. i'd rather play it on computer, but it might run better on the ps3.

Can't you overclock it a little?
I squeezed 25% more megahertzers out of my cpu with just a stock cooler.

I did some digging and it looks like the game runs at 27-30FPS on a PS3. Personally I think games running at 30FPS are close to unplayable, and it is a frame rate that will never improve with time like it might with a new PC. I would hope your PC could do better, but there is no way of knowing for sure outside of trying it. Different people have different ideas of what constitutes playable, and its hard to guess what the minimum system requirements will get you. I did find a report of one person with a better CPU and only slightly better video card getting 30-40FPS. I would guess you would get similar performance to the PS3, but I will not swear to that. I will say you will probably have more tweaking options.

You could try upgrade your CPU, but there is a good chance that, unless you are experiencing non-game processing issues, you may not feel like you got your money's worth with a CPU upgrade and it won't transfer to a new build like a video card will. If we are talking about gaming I think your video card is your biggest bang for buck upgrade option. If you had a higher end card I might say otherwise.

Other people might disagree(and ask around) but there is some good room for massive performance upgrades with little cost output. As someone who just did a CPU upgrade, but took a GPU downgrade, my system actually feels much, much slower. That said it probably would be worth starting over(if you go for a nice rig, or have a prebuilt system that doesn't upgrade well), but if it's going to be a year or more, then all the more reason to buy a better card since you can take it with you (ideally) and it could make waiting a year more comfortable. That's just what I would do in your situation.

If you do go for the CPU take a good look at what the Motherboard will take. Make sure the socket type matches, that your revision takes the CPU class (athlon, phenom II, ect) AND what max wattage it supports. There are some AMD quad cores that run at 125W and many boards only go up to 95W. Also be sure to remember that passmark website or find others that can show you what you have, vs what you are thinking about buying. If you haven't done much upgrading make sure you start a thread and ask people what to look out for. You don't want to buy anything you can't use.