Am I perfect (number)?

Java, 255 270 bytes (Still FF in base 17)

class C{public static void main(String[]a){int i=new Integer(a[0]),k=0,l=0;a[0]=" ";for(;++k<i;)if(i%k<1){l+=k;a[0]+=k+" ";}}System.out.print("I am "+(l==i?"":"not ")+"a perfect number, because "+a[0].trim().replace(" "," + ")+" = "+l+(l==i?" == ":l<i?" < ":" > ")+i);}}

And a more readable version:

class C {
    public static void main(String[] a) {
        int i = new Integer(a[0]), k = 0, l = 0;
        a[0] = " ";
        for(; ++k<i ;){
            if (i % k == 0) {
                l += k;
                a[0] += k + " ";
            }
        }
        System.out.print("I am " + (l == i ? "" : "not ") + "a perfect number, because " + a[0].trim().replace(" "," + ") + " = " + l + (l == i ? " == " : l < i ? " < " : " > ") + i);
    }
}

Previously didn't work for odd numbers, so I had to tweak a few things. At least I got lucky with the byte count again. :)

R, 158 163 157 153 143 141 bytes

Still room to golf this I think.
Edit: Replaced if(b<n)'<'else if(b>n)'>'else'==' with c('<'[b<n],'>'[b>n],'=='[b==n]). The paste(...) is replaced with an rbind(...)[-1]. Thanks @plannapus for a couple more bytes.

n=scan();a=2:n-1;b=sum(w<-a[!n%%a]);cat('I am','not'[b!=n],'a perfect number, because',rbind('+',w)[-1],'=',b,c('<'[b<n],'>'[b>n],'==')[1],n)

Ungolfed

n<-scan()             # get number from stdin
w<-which(!n%%1:(n-1)) # build vector of divisors
b=sum(w)              # sum divisors
cat('I am',           # output to STDOUT with a space separator
    'not'[b!=n],      # include not if b!=n
    'a perfect number, because',
    rbind('+',w)[-1], # create a matrix with the top row as '+', remove the first element of the vector
    '=',
    b,                # the summed value
    c(                # creates a vector that contains only the required symbol and ==
        '<'[b<n],     # include < if b<n
        '>'[b>n],     # include > if b>n
        '=='
    )[1],             # take the first element 
    n                 # the original number
)

Test run

> n=scan();b=sum(w<-which(!n%%1:(n-1)));cat('I am','not'[b!=n],'a perfect number, because',rbind('+',w)[-1],'=',b,c('<'[b<n],'>'[b>n],'==')[1],n)
1: 6
2: 
Read 1 item
I am a perfect number, because 1 + 2 + 3 = 6 == 6
> n=scan();b=sum(w<-which(!n%%1:(n-1)));cat('I am','not'[b!=n],'a perfect number, because',rbind('+',w)[-1],'=',b,c('<'[b<n],'>'[b>n],'==')[1],n)
1: 12
2: 
Read 1 item
I am not a perfect number, because 1 + 2 + 3 + 4 + 6 = 16 > 12
> n=scan();b=sum(w<-which(!n%%1:(n-1)));cat('I am','not'[b!=n],'a perfect number, because',rbind('+',w)[-1],'=',b,c('<'[b<n],'>'[b>n],'==')[1],n)
1: 13
2: 
Read 1 item
I am not a perfect number, because 1 = 1 < 13
> 

Python 2, 183 173 170 bytes

b=input();c=[i for i in range(1,b)if b%i<1];d=sum(c);print'I am %sa perfect number because %s = %d %s %d'%('not '*(d!=b),' + '.join(map(str,c)),d,'=<>='[cmp(b,d)%3::3],b)

Examples:

$ python perfect_number.py <<< 6
I am a perfect number because 1 + 2 + 3 = 6 == 6
$ python perfect_number.py <<< 12
I am not a perfect number because 1 + 2 + 3 + 4 + 6 = 16 > 12
$ python perfect_number.py <<< 13
I am not a perfect number because 1 = 1 < 13
$ python perfect_number.py <<< 100
I am not a perfect number because 1 + 2 + 4 + 5 + 10 + 20 + 25 + 50 = 117 > 100
$ python perfect_number.py <<< 8128
I am a perfect number because 1 + 2 + 4 + 8 + 16 + 32 + 64 + 127 + 254 + 508 + 1016 + 2032 + 4064 = 8128 == 8128

Thanks to xnor for saving 13 bytes!