we use MPLS link and router is 3745

On many Cisco routers, if CBWFQ is supported, you can map a class to the IP address of interest and reserve your 512 Kbps. If you're just doing logically point-to-point across MPLS, that would be enough. If, however, you're supporting multiple sites and allow any-to-any, you often encounter MPLS egress congestion. Since you don't control the MPLS egress router, your MPLS provider does, you'll need to discuss your requirement with your MPLS provider.

Many MPLS providers can offer QoS. You mark your traffic going into MPLS a certain way, and they can provide some guarantee of egress bandwidth, e.g. they might guarantee a certain class will obtain 25% of your link, which if its a 2 Mbps link will provide your 512 Kbps.

Any documents which helps me in configuring this ?

1st make an ACL to match your destination ip

access-list 101 permit ip any host x.x.x.x

2nd make a class map to match the ACL

class-map myfavdestination

match access-group 101

3rd make a policy-map to match the class above with the QoS you want to give it

policy-map reserve512

class myfavdestination

bandwidth 512

4th attach the policy-map to the outgoing interface pointing to the SP

interface serial x/y

service-policy output reserve512

verify using "show policy-map interface serial x/y" if the class is being given the appropriate QoS levels.

Note: This is only a barebone config and you might need to work with your provider closely to set DSCP values if necessary to get the required levels

Arvind's post provides a clear example of how you might use CBWFQ. Much more information can be found by searching Cisco's site either using "CBWFQ" or "class based weigthed fair queue", e.g. http://www.cisco.com/en/US/docs/ios/12_0t/12_0t5/feature/guide/cbwfq.html