C#

[DllImport("kernel32.dll")]
public static extern void GlobalMemoryStatusEx(ref MEMORYSTATUSEX ms);	

public struct MEMORYSTATUSEX {
	/// <summary></summary>
	public int Length;			// DWORD
	/// <summary></summary>
	public int MemoryLoad;			// DWORD
	/// <summary></summary>
	public long TotalPhys;			// DWORDLONG
	/// <summary></summary>
	public long AvailPhys;			// DWORDLONG
	/// <summary></summary>
	public long TotalPageFile;		// DWORDLONG
	/// <summary></summary>
	public long AvailPageFile;		// DWORDLONG
	/// <summary></summary>
	public long TotalVirtual;		// DWORDLONG
	/// <summary></summary>
	public long AvailVirtual;		// DWORDLONG
	/// <summary></summary>
	public long AvailExtendedVirtual;	// DWORDLONG
}

private void currencyTextBox_TextChanged(object sender, EventArgs e)
{
    imageProgress.Visible = true;
    Application.DoEvents();

    ... // Processing

    imageProgress.Visible = false;
    Application.DoEvents();
}

using System;
using System.ComponentModel;
using System.Drawing;
using System.Windows.Forms;

public class BusyTextBox : TextBox
{
    private Image busyImage;
    private bool isBusy;

    public Image BusyImage
    {
        get { return busyImage; }
        set { busyImage = value; }
    }

    [DesignerSerializationVisibility(DesignerSerializationVisibility.Hidden),
    Browsable(false)]
    public bool IsBusy
    {
        get { return isBusy; }
        private set
        {
            isBusy = value;
            if (value)
            {
                using (Graphics g = this.CreateGraphics())
                {
                    // draw image
                    // g.DrawImage(busyImage,
                }
            }
            else
            {
                Invalidate();
            }
        }
    }

    protected override void OnTextChanged(EventArgs e)
    {
        IsBusy = true;
        // Do Your DB Stuff
        base.OnTextChanged(e);
        IsBusy = false;
    }
}